Early in World War II the primary instrument for delivering naval combat power became the aircraft carrier. The reason was range: aircraft could deliver a concerted attack at 200 miles or more, whereas battleships could do so only at 20 miles or less. The foremost tactical question during the transition in the 1920s and ’30s was whether aircraft could lift enough destruction to supersede the battleship. Into the 1930s skeptics were correct that aircraft could not. But by the end of that decade, engines were carrying adequate payloads, dive-bomber and torpedo-plane designs had matured, carrier arresting gear and associated flight-deck handling facilities were up to their tasks, and proficient strike tactics had been well practiced. U.S. and Japanese naval aviators were pacesetters in these developments.

There was a subordinate tactical question as well: could the enemy be found at the outer limits of aircraft range? The ability to attack fixed targets such as the Panama Canal or Pearl Harbor, and to achieve surprise in doing so, had been amply demonstrated in naval exercises as well as in battle, but finding, reporting, and closing on ships at sea was a greater challenge. Without detracting from the courage and skill of aviators, it may be said that effective scouting was the dominant tactical problem of carrier warfare and had utmost influence on the outcomes of the crucial carrier battles of the Pacific Theatre in 1942: the Coral Sea (May 4–8), Midway (June 3–6), the Eastern Solomons (August 23–25), and the Santa Cruz Islands (October 26). In those closely matched battles the quality of U.S. and Japanese aviators and their planes was virtually on a par. When the United States won, it did so by superior scouting and screening, owing in large measure to air-search radar and to the advantage of having broken the Japanese code.

The command and control structure polished by the U.S. Navy during the war was the third vital component, after scouting and the delivery of firepower. The tangible manifestation of modern C² was the Combat Information Center, which centralized radar information and voice radio communications. By 1944 the tactical doctrine of coordinating fighter air defenses, along with the now much strengthened antiaircraft firepower on ships of the fleet, was so effective that in the Battle of the Philippine Sea (June 19–21, 1944) more than 90 percent of 450 Japanese aircraft were wiped out in a fruitless attack on Admiral Raymond Spruance’s 5th Fleet.

The new tactical formation was circular, with carriers in the centre defended by an antiaircraft and antisubmarine screen composed of their own aircraft plus battleships, cruisers, and destroyers. For offensive purposes, a circle allowed a rapid simultaneous turn by all ships in a task group in order to launch and recover aircraft. For antiaircraft defense, the circle was shrunk in diameter as tightly as possible so that each screening ship, by defending itself, helped defend its neighbour.

The new battle paradigm called for a pulse of combat power to be delivered in a shock attack by one or more air wings. Despite every intention, though, air strikes against alerted defenses were rarely delivered as compactly as practiced, nor were they as decisive tactically as naval aviators had expected. In the five big carrier battles, one attacking air wing took out an average of only one enemy carrier. (Viewed strategically, this average, along with losses of aircraft of around 50 percent per battle, was enough to govern the pattern of the Pacific war.) Since it took more than two hours to launch, marshal, and deliver an air strike, it was difficult to attack before an enemy counterstrike was in the air. Successful command at sea depended as never before on effective scouting and communication, because in order to win a decisive battle, in World War II as in all of naval history, it was necessary to attack effectively first.

Dominant though it was, carrier-based air power did not control the seas at night. With a modicum of success, the high-quality ships of Germany exploited the hours of darkness, especially during the winter months and in northern waters. In the bitterly contested campaign for Guadalcanal in the fall of 1942, guns ruled supreme at night and very nearly tipped the balance in favour of Japan. Expecting to be outnumbered as a result of the Five-Power Naval Limitation Treaty of 1922, the Imperial Japanese Navy had practiced night tactics assiduously in order, as they supposed, to whittle down the U.S. battle line during its slow march west across the Pacific. Having developed the matchless Long Lance torpedo, they installed it liberally in light cruisers and destroyers and developed tactics that would hurl a barrage of the long-range weapons in the direction of the enemy line—at the same time taking care not to expose the beams of their own ships to a counterstroke. Standard U.S. doctrine, on the other hand, called for fighting in column, employing guns as the primary weapon; the advantages that should have accrued to the Americans at night from superior radar were largely squandered. Between August 1942 and July 1943, in the cruiser–destroyer battles of Savo Island, Cape Esperance, Tassafaronga, Kula Gulf, and Kolombangara, Japanese night tactics prevailed. Not until mid-1943, with tactics attributed to Captain (later Admiral) Arleigh Burke that exploited the radar advantage in full, did the U.S. Navy redress the balance.

Still, naval aircraft were the weapons of decision. Although the duels of the great carrier fleets received more attention, air strikes from sea to shore were as crucial in securing control of the seas. Strikes by the British at Taranto, Italy (November 11, 1940), by the Japanese at Pearl Harbor (December 7, 1941), and by the Americans in the South Pacific at Rabaul (November 5 and 11, 1943) and Truk (February 17–18, 1944) were as important to that end as were the more sensational fleet engagements.

Also, in 1944 and 1945 the U.S. 3rd and 5th fleets, 27 fast carriers strong, took the war successfully against entire complexes of airfields in Formosa (now Taiwan), the Philippines, and Japan itself. A traditional tactical maxim, “Ships do not fight forts,” was suspended for the duration of the war.

In the closing days of the war in the Pacific, the Battle of Okinawa served to indicate the nature of future combat at sea. By that time the U.S. Navy had reduced the Japanese Navy to impotence, and manned aircraft could not penetrate the sure American defenses. Nevertheless, during the three-month campaign for Okinawa (April–June 1945) the U.S. Navy lost 26 ships and suffered damage to 164 more—this time to Japanese kamikazes (suicide pilots) flying out of airfields in Japan. The pilots who flew these one-way missions were delivering, in effect, human guided missiles. Kamikazes showed that missiles could, on sufficient occasion, get through otherwise impenetrable defenses. The missile-guidance technology exhibited in the late stages of the war in Europe indicated that missiles would be the kamikazes of the future. And the atomic bomb offered the ugly threat of “one hit, one kill” at sea.