Photograph of initial moments of Pearl Harbor attack

Naval History and Heritage Command #NH 50930

Surprise characterized both the beginning and the end of the Pacific War. The surprise attack on Pearl Harbor ensured that there would be no early move by the U.S. Pacific Fleet into the western Pacific. The nuclear attacks also relied on surprise, since they were conducted by small groups of unescorted, lightly armed "Silverplate" B-29s that the Japanese assumed were observation flights.

Surprise is achieved by an attacking force when the defenders are brought under fire before they are aware of the threat. It gives the attacker three important advantages. First, the defender is usually not concentrated against the attack. This gives the attacker a more favorable force ratio at the key point. Second, the defending forces are usually not fully alert and will thus be slower to respond to the attack. Third, the psychological shock of the unexpected attack can be detrimental to the defenders' morale.

The Pearl Harbor attack caught the U.S. Pacific Fleet with its antiaircraft guns unmanned and many of its ships not buttoned up. The harbor defenses were also unmanned and there were no fighters in the air. Indeed, many of the aircraft were parked in the open, vulnerable to attack, because of exaggerated concerns with sabotage. This meant that the first Japanese wave was able to launch its attack almost unopposed, and many of the ships that were hit by torpedoes (such as California) quickly flooded because their watertight doors were not dogged down. Thus a smaller (but superbly trained and equipped) Japanese force was able to cripple the battle line of the Pacific Fleet with little loss.

The nuclear attacks likewise were able to reach their drop points unopposed because the Japanese did not consider them a significant threat. In this case, the surprise was partly technical: Although the Japanese did some nuclear research during the war, and were aware of the potential of nuclear power, they did not expect their enemies to field a working nuclear bomb before the end of the war.

Surprise can also be achieved by a defender. Sometimes this is inadvertent, as when the Allied airborne assault on Arnhem in Europe was thrown back by panzer units that had been moved into the area for rest and refit just before the attack. In the Pacific War, the first assault on Wake was thwarted through a deliberate use of surprise: The defenders had carefully camouflaged their coastal defense guns, and did not open fire until the Japanese landing ships had closed to point blank range. Los Negros in the Admiralties is an intermediate case: The Japanese defenders had concealed their numbers and were deployed against an invasion, but at the wrong spot.

Surprise can be thwarted through good intelligence and thorough reconnaissance. The Pearl Harbor attack succeeded because the American intelligence organizations had their attention fixed on the Philippines, where a Japanese attack was in fact imminent, while the commanders at Pearl Harbor had a faulty air search plan that extended further than necessary towards the Marshall Islands and left the northern approaches to Oahu uncovered.

Surprise can also be mitigated in land warfare through the use of reserves. These are mobile formations kept back from the main battle line that can be rapidly deployed to a threatened area of the front. This allows the defender to recover quickly from any initial local surprise. The defending commander must carefully judge how much of his force to pull into reserve and how far back from the front to place it. A rule of thumb is to place one-third of his force in reserve at a distance behind the front equal to half his frontage. Thus, a division commander defending ten miles of the front line would place two regiments on the line and pull the third regiment into reserve about five miles behind the front line. Too much force in reserve left the front line weak and risked penetration before the reserves could arrive; too little force was inadequate to reinforce a threatened point. Likewise, a reserve far behind the front line would take too long to reach the threatened point, while a reserve very close to the front line might find itself pinned down by holding attacks before it could move to the enemy's Schwerpunkt or point of maximum effort.

Tactical and Strategic Surprise. Surprise can be either tactical or strategic, depending on whether it takes place on the local, tactical level or at the operational level. Allied forces in the Pacific generally used deception to attempt to achieve strategic surprise, but made decreasing efforts to achieve tactical surprise as the war progressed. It was felt that thorough reconnaissance and heavy preliminary bombardment were more important than achieving local surprise.

Guarding Against Surprise. The most elementary precaution for avoiding surprise is to go to a high state of alert. Unfortunately, troops on constant alert soon become exhausted, and their training and morale suffers.

Warships typically have several alert postures depending on the perceived level of threat. Ships in a secure rear area port are at their lowest level of alert, and very often are carrying out repairs and preventative maintenance that interfere with watertight integrity. California was sunk during the attack on Pearl Harbor, in spite of the failure of two torpedo hits to penetrate her underwater protection, because several hatches to the void spaces of the underwater protection system had been opened for inspection.

Warships at sea generally maintained port and starboard watches, in which the two halves of the crew alternated four hour watches. This ensured that the most critical stations were manned in case of a surprise attack. Warships also generally set Condition Yoke, in which the most critical watertight doors and hatches were shut, leaving the remainder open for improved habitability and to allow the crew to rapidly man their stations if needed. When combat was imminent, a warship went to General Quarters, in which the entire crew manned their battle stations and Condition Zed (maximum watertight integrity) was set.

The ability to rapidly go to General Quarters and set Condition Zed was crucial for recovering from surprise at sea. Japanese airmen participating in the attack on Pearl Harbor were impressed by how rapidly the Americans manned their antiaircraft weapons; a U.S. battleship could generally set General Quarters in less than ten minutes, which was apparently less than the time the Japanese were accustomed to. Unfortunately for the Americans, ten minutes was not enough warning to prevent the Pearl Harbor disaster.


Cohen (1949)
Morison (1958)

Zimm (2011)

Valid HTML 4.01 Transitional