While Germany, Japan and Italy all fielded large land armies, and powerful air forces, the biggest oversight by all three was in the proper development, and use of naval power.
The biggest naval warfare failure. Germany had built highly advanced surface warships, and had the industrial capacity to build fleets. They simply didn’t do it.
Hitler, and Kriegsmarine chief Admiral Erich Raeder realized the need for a battle fleet. However, as the land war expanded in Europe, Hitler became less and less interested in naval matters.
Germany by September 1939, had built advanced warships comparable, or superior to any navy in the world. But in such few numbers, Germany couldn’t assemble one effective battle-group that could survive combat beyond the Baltic Sea.
Even Germany’s infamous U-boat fleet barely existed in 1939, with a mere 17 vessels in commission. And, until the very end of the war, Germany did not build a true ocean-going U-boat.
Italy’s Regia Marina, was actually quite powerful. Most of its battleships and cruisers were fairly modern, heavily armed, fast, and highly maneuverable. Italian sailors were as well-trained, motivated and professional as those of any modern navy.
The problem, was the Italian admiralty’s mortal fear of the British Royal Navy. Despite successes against the British, they never fully prosecuted clear openings to decisive victories. For the most part, Italy’s main battle fleet was kept in port.
With land based air cover, the Italian battle fleet could have provided powerful naval gunfire support to Axis forces in North Africa, and stood a fair chance against Britain’s Mediterranean Fleet.
One major Italian accomplishment was the December, 1941 Italian raid on Alexandria, Egypt by six frogmen operating manned torpedoes. They managed to sink the battleships HMS Valiant, and HMS Queen Elizabeth in shallow water, putting both out of action for over six months.
Despite Japan’s foresight with naval air power, they entirely failed to appreciate other facets which led to a rapid collapse of Japan’s naval supremacy after the Battle of Midway.
Japan had a fleet of large modern submarines (a few reaching the size of destroyer), with the range to operate off the US West Coast, yet never duplicated German Wolf Pack tactics against American merchant shipping, or even warships.
For still mystifying reasons, Japan refused to embrace the convoy system for protection of merchant shipping until far too late. American submarines patrolled nearly unopposed and by early 1945 had effectively annihilated Japan’s Merchant Marine.
Japan also failed to embrace standardized capital warship designs; or to make combat air groups interchangeable between aircraft carriers; and never operated their large fleet of surface combatants with land based air cover. Had they done so during the Battle of Leyte Gulf, Japan would likely have destroyed General MacArthur’s landing force.
Most devastating of all, was Japan’s tardiness establishing a naval aviation training command. They shockingly did not have one, until after the Battle of Midway. The result was that Japan had no hope of rebuilding the elite naval air force lost at Midway, before final defeat.
Implementation of Japan’s Kamikaze strikes, while sinking smaller warships, and taking many lives, never posed a fatal threat to capital ships. Late in the war, Japan very nearly sank the brand new Essex Class aircraft carrier Franklin, with a purely conventional attack by one dive bomber.
Two armor-piercing bombs struck home, gutting the ship and putting it out of action for the rest of the war. The Japanese pilot, flew home safely.
Naval warfare against the Axis, was by no means a pleasure cruise. It cost many Allied lives and much fortune in ships, and materials. However, it would have been far, far worse had the Axis powers not so severely neglected and failed to prosecute, proper naval warfare tenets of the 1940’s.