May 122012

The U.S. Navy’s “Special Weapons Ordnance Device” (SWOD) Mark 9 “Bat” glide bomb was one of the world’s earliest fully-automatic, target-seeking “smart” weapon systems. The Bat was a development of the “Pelican” glide bomb, which was equipped with a Receiving Homing Beacon (RHB) that required a radar beacon to illuminate the target. The Bat had an S-band search and homing radar which had a search range of approximately 25 nautical miles (nm) and could lock on a target at about 10 nm. The Naval Air Modification Unit (NAMU) conducted the first tests of the Bat in 1944; after 10 flights in the fall of that year, the glide bomb was put into production. Thirty-five drops were made under combat conditions in 1945, resulting in a total of 4 direct hits. This relatively low percentage of hits was attributed to the inexperience of the operational personnel and malfunction of some of the guidance and control components. Further tests conducted by the Navy in the fall of 1945 resulted in hits in the 60-65% range, which was considered to be fairly good.

This article reproduces a U.S. Army Air Force (USAAF) report dating from September 20, 1945 on the operational and tactical suitability test of the Bat. The following paragraphs adapt the introduction to the report, which can be read in depth by clicking through the image gallery below. High resolution versions of the photos shown at left may be purchased for a small fee at the end of the article.

The object of the test (AAF Board Project No. Q 4785) was to observe the employment of the SWOD Mark 9 Bat by U.S. Navy PB4Y-2 Privateer squadrons against Japanese ships, and to report technique, results, and other pertinent details to the headquarters of the USAAF. The Army Air Forces Board furnished a liaison officer to observe use of the weapon by the Navy in the Pacific Theater.

Factual Data

The Bat was a radar controlled target seeking glider with a 1,000 lb bomb carried internally. The glide bomb was 11.5 ft long, had a wing span of 10 ft, and the fuselage was 2.5 ft in diameter at the largest cross section. The designed glide ratio was between 3.5 to 1 and 5.5 to 1. The Bat radar system was installed in the nose of the glide bomb to automatically track the pre-selected target and to furnish directional control signals to the glide bomb so as to cause it to home in on the target. The radar set was a functionally complete unit with its own transmitter and receiver. A suitable target was selected by the Bat operator, stationed in the mother aircraft, who had an auxiliary “A” scope, which displayed the target signals received by the Bat radar. The operator was aided in selecting the target by the operator of the search radar in the mother plane (AN/APS-2, in this case). Both the pilot and Bat operator also had a target left-right, up-down indicator, which was operated by the Bat video signals after the target had been locked. After the target was selected, the Bat operator locked the tracking circuits to this target when at a range of less than 15 miles. Thereafter, the Bat radar set tracked the selected target exclusively. The Bat was released from the mother plane when within certain range and altitude limits, and 180 kts speed or over. After the Bat was released, the radar set and the glider controls were operated on power from 3 storage batteries carried in the glider. After release, the radar set took over complete control of the glider, causing it to home in on the target.

The Bat was employed by one PB4Y-2 Privateer squadron (VPB-109) based in Palawan for a month and by this same squadron and two other PB4Y-2 squadrons (VPB-123 and VPB-124) based in Okinawa for 3 months. These 3 patrol bombing squadrons were the only squadrons with the SWOD Mk 9.

Data were gathered on the 33 Bats expended, from records or by personal observation by the AAF liaison officer. Preliminary observations were made of training carried out by Fleet Air Wing 2 at Kanehoe Naval Air Station, Oahu, T.H.


The observing Air Force liaison officer concluded the following:

  1. The SWOD Mk 9 Bat, in its existing form, was not suitable for combat use by the AAF.
  2. It was not sufficiently accurate for use against pinpoint land targets.
  3. The range of the automatic tracking system was insufficient.
  4. It was too difficult to pick out the exact target from among several adjacent targets on the SWOD scope.
  5. The Bat was satisfactory only for use against single ships or 2 or 3-ship convoys out in the open sea away from rocks and islands and other radar targets.


It was recommended that the SWOD Mk 9 Bat technical and operational information be made available to the Air Technical Service Command for evaluation and use in the developmental program of Air Force pilotless aircraft.

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Postwar Use of the Bat

While the Air Force never adopted the Bat, the Navy continued to employ the weapon (redesignated as the ASM-N-2) for several years after the end of WW II. According to the excellent (which I highly recommend for those interested in a more comprehensive history of the Bat and its offshoots), post-war Privateer crews maintained their proficiency with the glide bomb by attacking icebergs in the North Atlantic. An upgraded version of the Bat was fielded in 1953, but was withdrawn from service soon thereafter. Almost 3,500 weapons were produced under the Bat program, along with many government patents. It consumed 8 million man hours of research and cost nearly $850 million in 2012 dollars, which was only exceeded by the Manhattan Project during the WW II period. While it did not achieve spectacular successes during WW II, the Bat laid the foundation for the guided stand-off weapons which have proven to be so lethal and effective in modern warfare.

All images from NARA Archives II, College Park, MD, RG 341

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  One Response to “USAAF Evaluation of Navy SWOD Mk 9 Bat Glide Bomb (1945)”

  1. Very nice article, I suggest to search for more data about the early stages of unmanned aircraft development.

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