“The arsenal included larger tanks, more powerful artillery, faster fighter planes and new bombers.”

AMERICA’S ANTICIPATED INVASION of Japan ultimately proved unnecessary – the atomic bombings of Hiroshima and Nagasaki made sure of that.

Yet all throughout 1944 and 1945, Allied commanders were drawing up plans for the final assault on the enemy home islands. The campaign, which was codenamed Operation Downfall, would have been several times the size of the D-Day invasion, making it the largest amphibious attack in recorded history.

And while much of the military hardware America planned to throw into the fight had already been proven on or above the battlefields of Europe and the Pacific, the U.S. military was also gathering a whole new generation of war machines for the epic onslaught. The arsenal included larger tanks, more powerful artillery, faster fighter planes and new bombers.

Here’s a glimpse at some of this weaponry that (thankfully) never got the chance to see action in World War Two.

B-32 Dominator

Developed in tandem with the Boeing B-29, the B-32 Dominator was a four-engine, heavy bomber roughly equal in performance to that of the Superfortress. Unlike its much more famous cousin, B-32 faced a number of production delays related to its pressurized crew compartment. It only entered service in limited numbers by the summer of 1945. Capable of hauling a 20,000-pound payload nearly 4,000 miles (6,400 km) at an altitude of 30,000 feet (9,000 m), the Dominator would certainly have seen action in the Pacific had the war continued into 1946. But with Japan’s surrender in August, the manufacturer never got the chance to complete the 1,500 of the aircraft that were ordered by the U.S. military. Only 118 B-32s were ever built. None of them remain intact.

T-28 Super Heavy Tank

The T-28, dubbed the “Super-Heavy Tank,” was originally designed to be impervious to everything on European battlefields, including Germany’s mighty Tiger II; its main gun was expected to make short work of enemy concrete fortifications, like those found on the the Siegfried Line. But the Allies also hoped the massive armoured fighting vehicle would take part in the invasion of Japan. Also known as the T-95 105mm Gun Motor Carriage, the T-28 was 36 feet long and weighed nearly 100 tons (more than three times heavier than the workhorse M4 Sherman tank), but was without a rotating turret. Due to its immense size and weight, the T-28 had a top speed of only 8 mph (12 km/h), not to mention an impractical combat range of less than 20 miles (32 km). But its heavy 300-mm armour would have made it all but indestructible in the Japanese campaign. Tokyo surrendered before the roughly two-dozen T-28s that were ordered could roll off Pacific Car and Foundry assembly lines. In fact, only two models were finished by VJ day. One was dismantled shortly after Japan surrendered; the other was mothballed at a U.S. Army depot in the years after the war. It was restored in 1974 and is now on exhibit at Kentucky’s Patton Museum of Cavalry and Armor.

“Little David”

Like the T-28 tank, the U.S. Army’s Little David mortar was also expected to see action on Japanese battlefields. In fact, the towed 914-mm gun was designed specifically to obliterate the dense fortifications the Allies were expecting to encounter on the home islands. More powerful than Germany’s notorious Schwerer Gustav railroad gun, the 40-ton American weapon featured a 22-foot long barrel that could launch a 3,500-lb. (1,600 kg) shell a distance of 6 miles (10 km). But like the T-28 tank, the Little David never fired a single shot in anger; Japan quit before it saw action. A prototype of the massive mortar is on display at the Aberdeen Proving Grounds in Maryland.

F8F Bearcat

The fast and agile Grumman F8F Bearcat fighter plane was already in limited service with the U.S. Navy on VJ Day and would certainly have been used in conjunction with Allied Corsairs, Mustangs and Hellcats in Operation Downfall. Designed to fly from U.S. carriers, the first model Bearcat reached a top speed of 430 mph (678 km/h); while upgraded variants could fly even faster. A nimble fighter and a capable attack aircraft, the F8F would have been instrumental in ensuring American air superiority over Japan, while providing close air support to friendly forces on the ground.

F7F Tigercat

Another in Grumman’s series of carrier-based “cat” warplanes, the F7F Tigercat was a twin-engine, heavy fighter and attack aircraft with a top speed of nearly 500 mph (800 km/h) and a range of more than 1,200 miles (1,900 km). Armed with a devastating combo of four 20-mm cannons and an equal number of .50 caliber machine guns, the Tigercat featured a two-man crew consisting of a pilot and a radar operator. Although in service with the Marine Corps as early as 1944, no F7F ever saw combat during the Second World War — it would have been ready for action had the fighting continued beyond the fall of 1945, however. Grumman eventually manufactured more than 300 of the aircraft, several of which performed capably over Korea. Interestingly enough, the F7F was originally designated the “Tomcat,” but that name was later rejected for being sexually suggestive. The title would be recycled 30 years later for the F-14 fighter jet.

USS Midway

A veteran of the war in Vietnam and the 1991 Persian Gulf War, the first assignment of the USS Midway (CV-41) would have been part of the campaign against the Japanese home islands had Tokyo not thrown in the towel. The lead ship of the Midway-class and the first of the post war “super-carriers,” the vessel was commissioned just one week after Japan’s surrender. Had the fighting continued, the Midway would have carried as many as 100 fighters and attack aircraft into action along the Japanese coast, and sailed with the more than 40 other Allied carriers and flat-tops slated to take part in the massive invasion.

Battlefield Nuclear Weapons

The atomic bombs dropped on Hiroshima and Nagasaki were such a closely guarded secret, few involved in the initial planning of Operation Downfall even knew of the weapons’ existence. But as details of the bombs were revealed to top commanders in mid-1945, mission planners considered using the nukes to support ground combat operations in Japan. In fact, with production of more nuclear weapons expected to be complete later in the year, the Pentagon planned for up to seven of the bombs to be available for use in the campaign. Of course, Japan finally surrendered unconditionally on Aug. 15 following the first two bombings and no more nuclear weapons were dropped.

(Originally published in MilitaryHistoryNow.com on Marsh 24, 2014)