Assessing the Impact of U.S. Forces on Pearl Harbor Heeding Multiple Warnings on December 7, 1941

Scott Martin is a career U.S. Air Force officer who has served in a multitude of globally-focused assignments.  He studied Russian and International Affairs at Trinity University and received his Masters of Science in International Relations from Troy University.  He is currently assigned within the National Capitol Region. Divergent Options’ content does not contain information of an official nature nor does the content represent the official position of any government, any organization, or any group.

Title:  Assessing the Impact of U.S. Forces on Pearl Harbor Heeding Multiple Warnings on December 7, 1941

Date Originally Written:  October 27, 2021

Date Originally Published:  November 8, 2021

Author and / or Article Point of View:  The author believes that the U.S. did receive significant warnings on the morning of December 7th, 1941 before the Japanese attack on Pearl Harbor. If those warnings had been acted upon in a timely fashion, the author believes that it is likely that the U.S. could have mitigated some of the damage inflicted by the Japanese. However, this author contends that the limited warning time would not have been sufficient to completely defeat the Japanese raid, and thus, Pearl Harbor would still be the event that drew the U.S. into World War II. 

Summary:  A key “what if?” about the attack on Pearl Harbor centers on the lack of U.S. action on the two main warnings received that morning i.e. the USS Ward’s sinking of a Japanese submarine and the Opana Radar Station detection of the first wave of Japanese aircraft. Those warnings could have saved lives, but the limited warning time makes it unlikely the U.S. could have defeated the Japanese attack.

Text:  While most associate the Japanese attack on Pearl Harbor with the ultimate in surprise attacks, U.S. Forces did receive warnings of pending action, especially that morning. Chief among the warnings was the USS Ward sinking a Japanese mini-submarine at 0640L, nearly a full hour before the arrival of the first wave of Japanese aircraft. Additionally, at 0701L, an Army radar installation at Opana on the western part of the island of Oahu detected a large mass of possible inbound flying objects, later determined to be the first wave of Japanese carrier-based aircraft. What if the command at Pearl Harbor, instead of ignoring the warnings, decided instead that the Ward and the radar station were the indications of an imminent attack? 

The Ward’s  radioing in that it sank a Japanese sub at the entrance of the harbor was not the first report/sighting of a Japanese submarine that day. At 0357L, the minesweeper USS Condor, reported a periscope near Pearl Harbor during patrol[1]. That information was passed to the Ward for action. Also, U.S. forces throughout the Pacific had been on a war alert status for over two weeks. For most, that meant a likely Japanese strike against locations far to the west of Hawaii[2]. The accounts of the Ward fell into the trap of more warnings/sightings that leadership did not feel warranted additional responses. 

The reporting of the Ward might have increased warning for possible sub-related intrusions, which U.S. Navy Admiral (ADM) Husband E. Kimmel, Commander in Chief of the United States Pacific Fleet during the Japanese attack on Pearl Harbor, felt was a significant threat[3]. However, the sub sighting along might not warrant an increase in harbor air defense actions. The Opana Radar Station, powered on longer than its scheduled 0400-0700 shift, detected multiple inbound contacts to conduct additional training while they waited for transport to leave the station[4]. In the subsequent actions, the inexperienced radar operators, while able to determine several aircraft could be in route, could not positively identify the inbound tracks[5].  Another factor involves the Officer-in-Charge at the information center at Fort Shafter. Upon receiving the call from Opana, he did not seem unduly concerned, as he knew a flight of U.S.-based B-17 were due in that morning[6]. Thus, the first wave of Japanese carrier-based planes made their way towards the island unopposed. 

Where the impact of the Wards and any possible change in the assessment of the radar station reporting could have had on the events of that morning would start at approximately 0730L, when ADM Kimmel received the Wards report[7]. If ADM Kimmel had called for an increase in the alert status at that point, the fleet would have had nearly 15-20 minutes to prepare for any inbound aggressive actions. While that might not seem like a lot of time, especially on a Sunday morning, the Sailors on ship would have been able to ready their ship-mounted anti-aircraft guns. Of note is that the ships in harbor were preparing for a Monday morning inspection, meaning most of the hatches and doors were open, thus, some warning would see the crews batten down the hatches to secure the ships[8]. 

While the 15-20 minute warning does enable the readying of anti-aircraft guns and for hatches to be secured, it does not leave time for significant aircraft launching. While possible for some alert aircraft to take off, there would be little time for the ground crews to man or move most planes to more secure locations. The Japanese were also able to take advantage in the different threat perception between the U.S. Navy and the U.S. Army as U.S. Army Lieutenant General (LTG) Walter C. Short, Commander of the Hawaiian Department, deemed sabotage the greatest threat to the ground-based aircraft.  As such, the majority of the island’s fighters were parked wingtip to wingtip out in the open[9]. Additionally, most of the aircraft were on four-hour alert status, so minutes’ warning would make little impact[10].

A major factor in the confusion and lack of action on the reports from the Ward and the Opana radar station stemmed from the lack of poor communications between the Navy and Army commands. LTG Short did not receive notice of the Wards actions and ADM Kimmel did not receive word about the sighting from the radar station. While this disconnect speaks to larger communication issues, the shorter-term issue would be that if Kimmel and Short did speak on the issue of the submarine[11]. If Kimmel contacted Short following the submarine activity, and both men agreed to increase the alert, even with limited time before the Japanese planes entered Oahu airspace, more lives and materiel might have been saved. Given how quickly most Sailors and Soldiers scrambled to gun positions after the shock of the first wave and the response the second wave of Japanese aircraft, any pre-warning/alert before the first wave might have reduced American casualties/increased Japanese losses. 

While an earlier alert call from ADM Kimmel and LTG Short, from the time of the Wards actions and the reporting of many inbound aircraft would have further increased America’s defensive posture, it is still likely that the U.S. suffers losses at Pearl Harbor.  In this scenario the Japanese lose more aircraft and don’t inflict as much damage to the U.S. ships in harbor, while the damage to the aircraft parked on the ground remains. In this scenario Pearl Harbor remains a Japanese tactical victory, and the U.S. still enters World War II. However, people will recall the actions of the Ward and the Opana radar detection, and how much worse things might have been had the U.S. not acted on their reporting. 


[1] Slackman, M. (1990) Target: Pearl Harbor. University of Hawaii Press, Honolulu, p.74.

[2] Bar-Joseph, U. and McDermont, R.(2016) “Pearl Harbor and Midway: the decisive influence of two men on the outcomes.” Intelligence and National Security, Vol 31 (No.7), p.952. Most analysts at the time thought that the Japanese would attack either the Philippines, the Malay peninsula or other American island holdings in the Pacific.

[3] Slackman, M. Target: Pearl Harbor. P. 55. Of note, ADM Kimmel, prior to his assignment as Commander in Chief, US Pacific Fleet, held the rank of RADM (Two Star). The position was a 4-star billet, thus, he was addressed as ADM vs. RADM. After his dimissing from his position in the aftermath of Pearl Harbor, he reverted to his original 2-star rank (RADM). 

[4] Twoney, S. (2016). Countdown to Pearl Harbor. The Twelve Days to the Attack. Simon and Shuster, New York. P. XII.

[5] Ibid, P. 275. The radar operators, even as inexperienced as they were, would have been able to determine the presence of 50 airborne signatures, which, if reported to Fort Shafter, would have given the OIC pause, as the US was not sending near that many bombers to Hawaii that morning.

[6] Ibid

[7] Slackman, M. Target: Pearl Harbor, P. 76.

[8] Bar-Joseph and McDermont. “Pearl Harbor and Midway: the decisive influence for two men on the outcomes.” P. 954.

[9] Ibid

[10] Slackman, M. Target: Pearl Harbor, P.135.

[11] Prange, G. (1982) At Dawn We Slept. Penguin Books, New York, P. 497.

Alternative Futures / Alternative Histories / Counterfactuals Assessment Papers Japan Scott Martin United States World War 2