Imperial Japanese Navy

Imperial Japanese Navy was, in 1941., third strongest navy in the world. Its core were 10 battleships. While over 20 years of age – as was the case in all other major navies – these ships had received extensive reconstructions and modernizations. Four of them had a relatively high speed of 26 knots, having been originally constructed as battlecruisers. Most powerful units were battleships Nagato and Mutsu, which displaced 33 000 tons as constructed but by 1941. their standard displacement had increased considerably, to maybe 39 000 tons. They had speed of 25 knots post-reconstruction, with range of 5 500 nautical miles at 16 knots, and armament of eight 410 mm guns. Under construction were new battleships Yamato and Musashi, which displaced 70 000 tons with speed of 27 knots, range of 7 200 nmi at 16 knots, and armament of nine 460 mm guns.

Most important element of the Japanese Navy were aircraft carriers. Japanese naval command had placed particular emphasis on development of the naval aviation, and was the first in history to field carriers as a centerpiece of its fleets. Despite this, development of Yamato class shows that it did not wholly abandon the idea of battleship as a decisive naval unit. At start of the war, Japanese fleet had 13 aircraft carriers, and two were about to be finished. Of those, seven were actually bases for hydroplanes. As such, Japan only had six fleet aircraft carriers, plus two under construction. Most powerful operational units were Akagi and Kaga, carrying 66 and 72 aircraft, respectively. Other ships were smaller, and carrying 30 to 40 planes. Ships under construction, Zuikaku and Shokaku, were even larger, capable of carrying 72 aircraft each.

Japanese navy had a very powerful cruiser force. This was a consequence of the Washington Naval Conference, which had limited the displacement and armament of cruisers, but did not limit their quantity. Thus, Japan forcibly built cruisers and by 1939. had a very powerful force of 12 heavy and 28 light cruisers. Aside from those, Japanese Navy had 96 large and 40 small destroyers, 36 large and 22 small submarines, and a large number of auxilliary ships. In total, Japanese navy had almost 400 warships displacing 1 270 000 tons.

Japanese navy had very advanced torpedo armaments and tactics. Japanese warships utilized large Type 93 600 mm torpedoes with 500 kg warheads, whereas most other navies utilized 533 mm torpedoes with 300 kg warheads. These torpedoes also used compressed oxygen instead of compressed air, which allowed them to achieve effective range of 22 000 meters at 49 knots, while US Mark 15 achieved effective range of 4 000 meters at 46 knots. Japanese destroyers were also unique because they, in addition to torpedoes already in tubes, also had a reserve torpedo for each tube. Using these torpedoes, torpedo launchers could be reloaded in 20 minutes even in heavy sea conditions. Air-dropped torpedoes could be released from altitude of 300 meters and at speeds of up to 400 kilometers per hour.

Much like other major powers, Japan did not have separate air force. Instead, army and the navy each had their own air forces. Navy specifically had 1 685 aircraft in service at the outbreak of the war. These were very good, as the Japanese constantly copied the best foreign models before adding their own improvements. Therefore, their fighters, torpedo bombers and dive bombers were equal or better than the best of the foreign models. Japan also had a very advanced industry of optical devices, especially the night vision devices. On the contrary, their technology for underwater detection and radiolocation (such as radar) was primitive. This was caused in part by doctrinal issues, as the Japanese Navy was focused on the decisive battle and thus ignored auxilliary services such as minelaying, minesweeping and convoy protection, which will come back to haunt them in the second half of the Pacific war.

Army had, in the beginning of the war, 1 700 000 men, but only 12 best divisions were used in the conquest of southeastern Asia. Far more were required to hold it. In 1941., Imperial Japanese Army contained 51 division, of which 27 were stationed in China and further 13 defended the Manchurian-Soviet border. The Second Sino-Japanese War will see a more or less constant deployment of over a million men between 1941. and 1945., which in 1945. amounted to about a fifth of its total manpower. Army also had its own air force, numbering some 3 000 aircraft. Japanese military personnel underwent a very strict, harsh and technically extensive training. Navy specifically chose nothern seas for its training, both for operational security – lack of merchant traffic meant that training could be done in secrecy – and also because harsh weather made performing duties much more difficult. This training led to high rate of casualties, but over time the Japanese Navy achieved a very high level of competency. Such harsh training however also meant that it was extraordinarily difficult to replace wartime losses, and with time the once extremely competent personnel will end up being replaced by personnel who did not have even the basic skills necessary for combat.

Pilots had at least 500 to 800 hours of flying, of which much was in combat operations during the war with China. Powerful propaganda also meant that the Japanese troops typically fought to death, and defended their positions to the last man. Quality of officers however was significantly inferior to those in US and European armies, both in formal education and in general knowledge of world events. Behaviour of the officers towards the troops was generally harsh and inhumane, which unsurprisingly translated to the equally inhumane treatment of prisoners.

United States Navy

United States Navy was the primary – and, thanks to events in Europe, effectively only – opponent that the Imperial Japanese Navy would have to contend with. On paper, the US Navy was larger and more powerful than the Imperial Japanese Navy. Its weakness however was that it had to be separated into the Atlantic and Pacific fleets, and only the latter could be used for defense against Japan. Yet the US Navy had a massive advantage over the Japanese Navy because it had, when the war started, a significant number of new ships under construction. United States also had an extremely strong industry, accounting for 41,7% of total warmaking potential in 1937., compared to Japan’s 3,5%.

	Japan	US Pacific 1941	US total	US building
Battleships	10	9	15	10
Aircraft carriers	6	3	6	12
Hydroplane ships	7	3	4	3
Heavy cruisers	12	13	18	8
Light cruisers	28	11	19	48
Destroyers	96	80	136	170
Old destroyers	40	0	49	0
Large submarines	36	40	49	29
Submarines	12	20	65	2

The core of the US Navy consisted of 15 very old but still very powerful battleships, which had been reconstructed and modernized multiple times. They were generally larger than the Japanese equivalents, displacing 32 000 to 34 000 tons, but were also 2 knots slower on average. Majority were armed with 356 mm (14 in) cannons, with three newest battleships (West Virginia, Colorado, Maryland) being armed with 8 cannons of 406 mm (16 in). Battleships under construction were much larger, faster and more powerful, but did not approach the size or power of the Japanese Yamato class.

US aircraft carrier were far larger and faster than the Japanese counterparts. Lexington and Saratoga had an official displacement of 33 000 tons (34 000 metric tons), but in reality were closer to 36 000 tons standard displacement, and could carry 90 modern aircraft each. Small (14 500 tons) carrier USS Ranger was in the Atlantic. Most modern carriers were three units of the Yorktown class with 19 800 long tons of standard displacement, carrying 80 – 85 aircraft each. Of these, Yorktown and Wasp were both in the Atlantic, and only Enterprise was in Pearl Harbour. Last Yorktown class carrier, USS Hornet, was fitting out at Norfolk Virginia. Additional 11 units of the Essex class had been ordered, but only USS Essex herself had been laid down (in April 1941).

Important characteristic of the US Navy was a very large number of destroyers, which allowed it to lease 50 old destroyers to the Royal Navy at beginning of war in Europe, thus providing assistance in the most critical phase of battle for Britain. In 1941., US navy had 171 destroyers and about as much under construction, and additional 200 destroyers were ordered after the attack on Pearl Harbour.

Like Japan, combat aircraft were divided between the Army and the Navy. Navy had around 5 000 aircraft, of which 3 200 combat aircraft. US fighters were inferior to Japanese Zero, but heavy bombers were far superior to Japanese equivalents while medium-weight bombers, dive bombers and torpedo planes were roughly comparable. US Navy had generally more strongly built ships than the Japanese navy. Technical education was good, but discipline and general training was inferior to Japanese and European navies alike. Naval gunnery science was very well developed, but the torpedo warfare was not given much attention, which caused many deficiencies on both techical and tactical levels. Ships were well constructed, and large distances of the Pacific ocean meant that significant attention was given to damage control procedures and the ability of ships to carry out repairs on sea. While US Army had been expanded to some 1 500 000 men in 30 divisions by mid-1941., these units were still undergoing training, and thus US garrisons on advanced positions such as Phillipines were very weak. US Army had some 7 000 aircraft, but only 1 500 of those were moden combat aircraft, with the rest being either support aircraft or so outdated as to be irrelevant in combat.

Pre-war US military was characterized by weak discipline, insufficient combat readiness of units, and slow and irregular delivery of war materials. However, thanks to the US economic power which was located far from any combat theatres, situation quickly changed and by January 1942. US industry was delivering 2 900 aircraft per month.

• modern
• World War 2