Julius Caesar planned to invade Parthia in 44 BC. It was to be a massive endeavor with the largest force he had ever led: 16 legions and 10,000 cavalries, in addition, to support troops. As a preliminary, he planned to first invade and conquer the kingdom of Dacia, roughly modern Romania, which he calculated could be accomplished by the end of 44 BC. The following spring, he would move on to Parthia.
Parthia was no pushover, as evinced by the Battle of Carrhae in 53 BC, where a Parthian cavalry force of 10,000 had all but annihilated a much larger Roman army of roughly 50,000, led by Caesar’s fellow Triumvir, Crassus. In 38 BC, Mark Antony invaded Parthia with an even larger force than that which Caesar had planned to use, numbering over 100,000 legionaries, 24,000 auxiliaries, and 10,000 cavalry, only to meet with disaster.
However, neither Crassus nor Mark Antony were in Caesar’s league as generals, while Caesar was Caesar – an all-time great military mind. And Parthia was not invulnerable to a Roman army led by a commander of genius. A century and a half later, the emperor Trajan did exactly what Caesar had planned, conquering Dacia, then successfully invading and defeating Parthia, seizing its capital city of Ctesiphon, annexing Mesopotamia, and dictating a highly favorable peace treaty.
It is not inconceivable that Caesar could have accomplished the same in the 40s BC. However, he would never get the opportunity to try: three days before he was to leave Rome for the Parthian campaign, Caesar was assassinated by Roman senators.
Between 1803 to 1805, Napoleon Bonaparte assembled and trained an army of 200,000 men near Boulogne, named the “Army of England” for its intended purpose of invading and conquering that country, and had built a large flotilla of barges to ferry it across. Control of the English Channel during the crossing was a prerequisite for launching the invasion – as Napoleon put it: “Let us be masters of the English Channel for six hours, and we shall be masters of the world” – but that was no easy task, given the Royal Navy’s superiority over Napoleon’s Franco-Spanish navy.
While the Army of England was drilled, trained, and honed to a fine edge across the narrow waters separating it from its target, Napoleon’s admirals tried to wrest temporary naval control over the English Channel to secure a safe crossing. The Franco-Spanish navy was divided into two main contingents, penned in and blockaded by two powerful Royal Navy fleets in Toulon and Brest. A third British fleet guarded the English Channel. The Royal Navy’s confidence was such that the First Lord of the Admiralty commented in response to invasion fears that: “I do not say they cannot come – I say they cannot come by sea“.
Napoleon’s admirals had to break out of their blockade in Toulon and Brest, combine the newly freed fleets, then fall upon and defeat the Britsh Channel fleet, or at least ward it off of a stretch of the English Channel long enough for the invasion force to cross the waters to England. To that end, a plan was hatched for the Franco-Spanish fleets in Brest and Toulon to  slip past the British,  sail to the Caribbean, [3 ] elude the pursuing British and ditch them somewhere in the Caribbean,  link up and unite forces near Martinique,  sail the fleet, whose combined strength should now be stronger than that British fleet guarding England, to the English Channel, and  establish temporary naval superiority over the English Channel long enough to safely transport Napoleon’s army to England.
It was an ambitious plan, the kind that Napoleon liked with rapid movements that trick a superior enemy into a reaction that leaves his forces dispersed, providing an opportunity for a sudden concentration against part of the enemy’s forces. However, that was easier done on land, where a general could estimate marching times over known distances with enough accuracy to concentrate at an opportune time and place. It did not work as well for naval operations during the age of sail, because the vagaries of wind and weather made it difficult to time a concentration of fleets with precision.
As the plan worked out in practice, the Toulon fleet broke out of its blockade in March, 1805, eluded the British fleet commanded by Horatio Nelson, and raced to the Caribbean. In the Caribbean, it managed to lose and ditch the pursuing Nelson, then sailed to the rendezvous off Martinique to link up with the Brest fleet. However, it was stood up, because the other fleet failed to breakout and was still blockaded in Brest, and so it sailed back to Europe. Off Spain, it was defeated in the Battle of Cape Finisterre in July, 1805, and was forced to flee to Cadiz, where it was blockaded.
With the plan to control the English Channel in tatters, Napoleon gave up on the invasion, and in August 1805, transformed the finely trained Army of England into the Grande Armee, and marched it from the Channel coast to Central Europe to fight the Austrians and Russians. Months later, the Franco-Spanish fleet was defeated decisively at the Battle of Trafalgar, but by then the army that had trained for years to invade England was fighting in Central Europe, hundreds of miles from the English Channel.
After the opening months of movement and maneuver warfare, WWI on the Western Front stagnated into gridlock as exhausted armies dug in where they stood. By the end of 1914, millions of soldiers faced enemies across no-man’s land while hunkered in trenches that stretched for hundreds of miles from the Swiss border to the English Channel. Direct attacks on entrenched opponents typically resulted in advances of a few hundred yards, or a few miles at most, and produced little other than mutual attrition, with attackers suffering significantly higher casualties commensurate with their greater exposure in the open to concentrated machine gun and artillery fire as they traversed no-man’s land.
Operation Hush in 1917 was a British plan to take advantage of Allied naval supremacy, cemented by the Royal Navy’s strategic victory in the Battle of Jutland the previous year. It aimed to outflank the Germans with an amphibious landing on the Belgian coast, behind the German trenches’ northern terminal on the English Channel. The horrors of trench warfare in that stretch near the coast were exacerbated by marshy ground that reduced the area to a sea of mud.
The idea was to first attack the German trenches with a normal ground assault across the area’s flooded no-man’s land. Once a sufficient advance had been made, such that a breakthrough out of the muddy region and into the dry land beyond was attainable, the British would land a force on the coast behind the enemy trenches, which would then wheel right and attack the rear of the Germans resisting the initial attack from Ypres. Pinched front and rear, the Germans defenses would crumble, and the British would advance over them to link with the amphibious force on dry land. With the muddy region which had made advance so difficult now behind them, and open dry land ahead, the British would have better prospects for future operations.
Unfortunately, the Germans grew suspicious and launched a spoiling attack in July, 1917, that pushed the British back. When the main British attack finally came, the Third Battle of Ypres in October of that year, it had to make an even greater advance than the planners of Operation Hush had envisioned. First, it had to recapture the ground taken by the Germans in July. Then, continue until close enough to the beaches where the amphibious force would land. The British failed to advance far enough to come within striking distance of a linkup with an amphibious force-landed behind German lines, so Operation Hush was cancelled.
Case Green was the German plan to invade Czechoslovakia in 1938. If it had been executed, WWII would probably have started a year earlier, and Germany would likely not have fared as well as she did in 1939 and 1940. The plan was an all or nothing gamble that would have pitted 37 divisions to attack the heavily fortified Czechs while leaving only 11 divisions to protect Germany from potential French and/or Polish attacks. At the time, Poland had a million-man army, while the French had nearly a million men on the Maginot Line alone, aside from their field army. Britain could quickly throw in another 200,000, with hundreds of thousands more over the following months.
Additionally, in 1938 Germany had not completed her rearmament, so her military was not yet the juggernaut unleashed on Poland in 1939 and against Western Europe in 1940. The Luftwaffe lacked the ability to strike Britain in 1938, the Kriegsmarine had few submarines, and the Wehrmacht as yet had few of the signature tanks that would spearhead the blitzkrieg in 1939 and 1940. So risky was the plan that German generals plotted to assassinate Hitler if the order to launch Fall Gruen was issued.
Unfortunately, Hitler ended up annexing Czechoslovakia without a fight because the Western Allies chose appeasement rather than confrontation, and sold out the Czechs in Munich in exchange for Hitler’s promises to behave. When Hitler broke his Munich promises and war broke out less than a year later, Germany was in a stronger position, and the Western Allies were relatively weaker. In 1938, the Allies would have fought while benefitting from the Czechs, whose well-trained and well-equipped military was hunkered behind strong fortifications and was supported with a formidable domestic armaments industry.
In 1939, the Czech military was no longer an asset in the Allies’ column, and the Czech armaments industry was churning out weapons for Germany. Indeed, a significant portion of German armaments during the war, especially early in the war, came from Czech factories. E.g.; Czech tanks such as the 38(t) played a significant role in the German conquests of Poland, Norway, and Western Europe, with 6 Panzer divisions armed with the 38(t) until 1942.
After the German blitzkrieg through Western Europe culminated in France’s surrender in 1940, Hitler assumed that Britain would seek peace terms. When that did not happen, he ordered plans be drawn up for invading Britain, Operation Sea Lion. A prerequisite for success was German air superiority over southern England and the English Channel. Otherwise, between the Royal Navy and the RAF, an invasion force would get mangled at sea, and any survivors who made it to land would end up cutoff on isolated beachheads and quickly defeated.
The need to defeat the RAF as a preliminary to Sea Lion was the driving motive for the Battle of Britain, and during the summer and early fall of 1940, a battle of attrition raged over British skies. The Germans tried their best, and came close on more than one occasion, pushing the RAF to its limit, and past that at times. But Fighter Command kept managing to send up just enough pilots, exhausted and wearied but still game, to contest the issue and savage the attacking Germans.
In the end, the Germans blinked first. Realizing that the aerial supremacy necessary of Sea Lion’s success was unattainable, the Luftwaffe shifted to night time terror bombing, the Blitz, in a bid to break Britain’s national will and cudgel it into suing for peace. Sea Lion was shelved, the invasion of Britain was abandoned, and the Germans began shifting their forces to the east, in preparation for an attack on the Soviet Union the following summer.
However, it is likely that Sea Lion never stood a chance, and Britain was never as vulnerable to invasion in 1940-1941 as is commonly assumed. Whatever the outcome of the aerial Battle of Britain, Britain’s leaders knew early on that the Germans could not successfully invade because they lacked the shipping and landing craft necessary to transport and support an invasion force strong enough to subdue Britain. The main reason the Allies invaded France in 1944, rather than 1943 as American commanders wanted, was the lack of sufficient landing craft. That problem was even worse for the German in 1940-1941. British leaders kept that to themselves, however: the national spirit of defiance and public morale was high in the face of an “expected invasion”, and there was nothing to be gained from tinkering with that and possibly inviting complacency.
German Invasion of Switzerland – Operation Tannenbaum
After France surrendered in June 1940, Switzerland was completely surrounded by Axis-controlled territory. A major aim of the irredentist Nazis was to gather all ethnic Germans into a single country, and that included the German-speaking Swiss. Hitler appalled that the German-speaking Swiss felt stronger attachment to their French and Italian-speaking countrymen than they did to Germans, opined that “Switzerland possessed the most disgusting and miserable people“, and that the Swiss were “a misbegotten branch of our Volk‘. He considered democratic Switzerland an anachronism and ordered plans drawn for its conquest and absorption into the Third Reich.
The result was Operation Tannenbaum (see map, above), which envisioned a two-stage conquest with 21 German divisions, a force later deemed excessive and downsized to 11, plus 15 Italian divisions. First, conventional attacks from Austria, southern Germany, and occupied France, assisted by paratroops dropped behind Swiss lines, would overrun the lower-lying parts of Switzerland where most of the population and economic activity was located. To the south, Italians were to mount holding operations. Once the important parts of Switzerland were conquered, follow-up attacks were to be made against Swiss army remnants in the “National Redoubt” – a fortified zone in Switzerland’s mountainous south.
The plan likely would have succeeded. Much has been made of Switzerland’s mountainous terrain, and the Swiss army planned to take advantage of their topography by retreating into the mountainous part of their country. However, the overwhelming majority of the Swiss did not live high up in the mountains, but in the lower parts of the country in valleys and foothills that were readily accessible to attacking Germans. Cutoff up in the mountains, one can only guess how long the Swiss in the National Redoubt might have been able to offer sustained resistance.
Partisan and guerrilla warfare would have been an option. However, that would have required the Swiss to be markedly different from other Western Europeans whose countries were occupied, yet exhibited little willingness to risk the massive reprisals and atrocities the Nazis were willing to inflict on restive conquered subjects. Bad as Nazi rule was, the Germans did not treat Western Europe as atrociously as they did the Eastern European Slavs. Western Europeans thus never felt that their backs were to the wall and that they had nothing to lose, to the same extent as did, e.g.; the Soviets or Yugoslavs, who responded with a fierce and widespread partisan resistance that had no equivalent in Western Europe.
It is unlikely that the Germans would have treated the Swiss, whom they viewed as fellow Germans to be incorporated into their Reich as fellow citizens, with anything approaching the severity that triggered widespread resistance in the East, but would more likely have treated them better than they did other Western Europeans.
Fortunately, the order was never given. While it would have been emotionally gratifying for Hitler to invade, there was no immediate necessity: the Swiss had no aggressive designs and surrounded on all sides by Axis territory, there was no security threat of occupation by the Allies to use as a base for attacking Germany. Switzerland also had no resources that were not readily available to the Germans via trade, and the Swiss banking system, combined with Swiss neutrality, made the country a convenient center for currency exchange and other international financial transactions.
Scheduled for November 1945, Operation Olympic was to be the first stage of an Allied invasion of Japan, with the goal of securing the southern third of Kyushu, the southernmost of Japan’s main home islands. The seized territory would provide airbases for land-based aircraft, and serve as the staging area for an even bigger invasion, Operation Coronet in the spring of 1946, directed at Honshu, the largest and most populous of Japan’s home islands.
The operation was to commence with amphibious landings on three Kyushu beaches, but as was discovered after the war, the Japanese had accurately predicted US intentions and landing sites – Japanese geography was such that the only viable beaches for large amphibious landings were the ones selected by Allied planners for operations Olympic and Coronet.
The Allies would still have prevailed in the end: the resources committed to the operation dwarfed those of the D-Day landings in France, and included 42 aircraft carriers, 24 battleships, 400 destroyers and destroyer escorts, tactical air support from the Fifth, Seventh, and Thirteenth Air Forces, and 14 divisions for the initial landing. Casualties, however, would likely have been horrific. Depending on the degree of Japanese civilian resistance – and Japanese authorities were busy training even women and children to fight the invaders with spears and pointy sticks -, worst-case scenarios envisioned over a million Allied and tens of millions of Japanese casualties.
Olympic’s planners were unaware of the highly secretive Manhattan Project, and when the US successfully tested an atomic bomb in July, 1945, their game-changing potential was not fully understood by planners. Envisioned simply as “really big bombs”, they had nebulous ideas of using atomic bombs during the November invasion in support of the amphibious landings. Their use instead against Hiroshima and Nagasaki in August 1945, shocked the Japanese government back to its senses, ended the war, and eliminated the necessity for Operation Olympic and its expected butcher’s bill.
In 1945, as the war in Europe drew to a close, Winston Churchill was exasperated by Soviet intransigence regarding Eastern Europe, which Stalin clearly aimed to turn into a Soviet empire. Britain had gone to war in order to defend Polish independence, but at the war’s end, Stalin was riding roughshod over the Poles, keeping the third of their country he had annexed in 1939 in cooperation with the Germans, reducing them to a Soviet client state, and extinguishing their freedom and independence.
Churchill saw it as a matter touching British honor, so he ordered his generals to draw up plans for an attack on the Soviets soon as Germany surrendered, with the nebulous aim of pushing them back to the USSR’s borders, or at least forcing them to treat Poland fairly.
They presented him with Operation Unthinkable, whose title indicates what the generals thought of Churchill’s idea. Two versions were offered, an offensive and defensive one. The offensive envisaged a surprise attack on the soviets in July 1945, intended to force Stalin to give Poland a “fair deal”. The defensive envisaged a British defense of Western Europe after America withdrew from the continent. The Soviets had 10 million men available in the summer of 1945. They outnumbered the British and Americans in Europe 4:1 in men, and 2:1 in tanks – and superior tanks at that. The Allies had an advantage in the air, but even that was subject to challenge, as the Red Air Force by 1945 had formidable fighter and ground attack arms.
Moreover, the Soviet military by 1945 was not the hapless rabble it had been in 1941 when the Germans invaded, but had grown into a veteran and battle-hardened force that had won bigger campaigns against significantly greater opposition than the Allies had faced. In a nutshell, Churchill’s generals concluded that it would be ill-advised because far from being a pushover, the Red Army in 1945 was dangerous, vicious, and very big. If war broke out, it was more likely to end with the Red Army conquering all of continental Europe, rather than getting chased back to the USSR.
More importantly, it was pointed out that Britain on her own stood no chance against the Soviets, and the US had no incentive to attack them – especially not over Poland and Eastern Europe. Standing up for Poland might have been a point of honor for Churchill, but few in the British government, and fewer still in that of the US, thought Poland or Eastern Europe were worth an even greater war against the Soviet Union than the one they had just concluded against Germany.
Unlike Britain, America had never guaranteed Poland’s territorial integrity, nor had it entered WWII in order to defend Polish sovereignty. Presented with the preceding, Churchill grudgingly let the matter drop, and Operation Unthinkable was archived.
After his successful Inchon landings in September 1950, led to the collapse of the North Korean invasion during the Korean War, General Douglas MacArthur vigorously pursued the routed enemy northward up the Korean Peninsula. Despite repeated warnings, MacArthur blithely dismissed mounting evidence that China would directly intervene in the war if his forces approached the Sino-Korean border, and insisted that the Chinese would do nothing.
MacArthur turned out to be wrong, and soon after his forces reached the Yalu River marking the border with China, the Chinese began pouring across in the hundreds of thousands, successfully evading detection. They struck in November 1950, surprising MacArthur and catching him completely off guard, and within weeks had defeated and pushed his demoralized forces out of North Korea and back across the border into South Korea.
His judgment and estimate of Chinese reaction having been proven catastrophically wrong, and his forces chased back down the Korean Peninsula by the Chinese even faster than they had raced up in pursuit of the North Koreans, a humiliated MacArthur reacted with histrionics and insisted that atomic bombs be dropped on China. His plan was to drop up to 50 atomic bombs in Manchuria on Chinese cities, military concentrations, and communication centers, and to seal off the Korean Peninsula from China by creating a radioactive belt across Manchuria, stretching from the Sea of Japan to the Yellow Sea.
President Truman, whom MacArthur had confidently assured only weeks earlier that China would do nothing if his forces marched up to the Chinese border, balked, and declined to trust MacArthur’s further confident assurances that the Soviets would do nothing if the US dropped dozens of atomic bombs on their Chinese ally. When MacArthur publicly contradicted Truman’s position, he was ordered to clear any further statements on the subject with the State Department first. MacArthur violated those orders, and again challenged Truman publicly on the use of atomic weapons in the Korean war, so Truman fired him.
During the Cuban Missile Crisis in 1962, the Pentagon urged President Kennedy to invade Cuba in order to remove Soviet nuclear missiles from the island, and the Joint Chiefs of Staff unanimously agreed that a full-scale invasion was the only solution. They presented the Presidents with two versions: Oplan 316 for a full invasion, and Oplan 312 for aerial strikes to take out the missiles, followed by an invasion if necessary. The hawks, led by Air Force General Curtis LeMay, had a clear preference for Oplan 316, as they contended that there was no guarantee that airstrikes alone would take out all the missiles, or that one or more of the missiles would not be fired at the US.
Planners expected 18,500 US casualties in the first ten days of the invasion, assuming no nuclear explosions. However, unbeknownst to planners, the Soviet forces in Cuba had tactical nuclear weapons, and Soviet leader Nikita Khrushchev had preauthorized the Soviet commander in Cuba to use tactical nukes at his discretion if he deemed it necessary. As the crisis intensified, Khrushchev withdrew release authority and forbade their use without his express permission. However, whether the modified orders would have been followed, is debatable.
In practice, tactical nukes were dispersed throughout Cuba to various Soviet units, under the physical control of officers as low down the chain of command as captains. Soviet forces had drilled in the use of those weapons as part of their defensive plan, and in the heat of battle, the custodians of those weapons would have been under intense pressure as they were subjected to overwhelming US aerial strikes, naval bombardment, and ground attacks. It is not difficult to envision a desperate local commander in such a scenario, perhaps cut off from communications with higher authority, resorting to the tactical nukes at hand to save his command, or at least ensure that its demise did not come cheap: the Red Army, with victory in WWII only 17 years in its past, did not lack military pride or an ethos of defiance unto death.
If the Soviets used nukes in Cuba, the US intended an overwhelming nuclear response. Things could easily have escalated from there to a full-blown nuclear exchange that would have devastated both countries and Europe, irradiated the Northern Hemisphere, and set humanity back centuries. Luckily, President Kennedy resisted the pressure from his generals and admirals and relying on diplomacy, back channels, and blockade, successfully diffused the crisis without triggering WWIII.
During the Vietnam War, plans were drawn to end North Vietnamese infiltration into South Vietnam and support the insurgency there by taking out North Vietnam with a direct invasion. The plan, as described in On Strategy: A Critical Analysis of the Vietnam War, by Harry G. Summers, was reminiscent of the Normandy invasion. It called for landing an airborne division to the north and west of Hanoi to block off the approaches to the Hanoi-Haiphong region, accompanied by a seaborne invasion with three amphibious divisions landed on beaches in the Haiphong area.
The Haiphong force would then drive onto and Hanoi and linkup up with the airborne troops there. With the Hanoi-Haiphong area secured, outside support would be drastically curtailed as two major railroads from China would be severed, the country’s main seaport would be in American hands, and the lines of communications to the south would be interdicted. Starved of Chinese and Soviet arms, ammunition, and supplies, and cut off from a steady infusion of North Vietnamese manpower, planners expected that organized armed resistance in South Vietnam would soon wane and collapse.
While the plan stood a high chance of success against the North Vietnamese, it was deemed too dangerous because China would likely join the fray. At the time, only 15 years had gone by since the Korean War. In that war, US and allied forces had pursued the routed North Koreans all the way to the Chinese border, based on the mistaken belief that China would do nothing. That led to the unpleasant surprise of the Chinese jumping in and pushing American forces all the way back to South Korea.
If China directly joined the war in response to a US invasion of North Vietnam, things could easily escalate from there into WWIII, with the Soviets getting dragged in. And unlike the situation during the Korean War, the US no longer held an overwhelming nuclear superiority, as the Soviets by the second half of the 1960s possessed thousands of nuclear warheads and the means of delivering them to targets in the US. American interests in Vietnam were simply not worth the risk, and so the planned invasion of Hanoi-Haiphong was never carried out.