Striking enemy ships with airborne munitions became a priority after World War I. While the challenges were monumental at the time, the rewards for success were too great to pass up. However, bombs and torpedoes dropped by early naval strike aircraft stood little chance against armored warships bristling with AA guns. Faced with this, the United States Navy sought a solution based in some of the most advanced technology of the era.
At the beginning of World War II, radar was coming into service with British armed forces. England shared that technology with the United States, and in 1940 the US Navy coined the term “radar” as an acronym for “radio detection and ranging”. At the same time, television technology was being refined and incorporated into military applications.
The desperate arms race drove technology farther and faster than ever before, and by April 1945, the US Navy deployed the ASM-N-2 Bat radar-guided glide bomb, the first automated anti-ship weapon to be used in combat.
Enter the Dragon
The concept of a TV-guided weapon arrived even before America was at war, as the Radio Corporation of America (RCA) proposed an anti-ship weapon in January 1941 that leveraged RCA’s television technology. Nicknamed the Dragon, the weapon used a nose-mounted TV camera to allow its operator to guide the glide-bomb to its target. The system worked well from a mechanical standpoint, but the early TV guidance technology was wonky, and the Dragon proved inaccurate.
In 1942, the US Navy struggled to counter the U-boats operating off the Atlantic seaboard, and a radar-guided bomb seemed a good solution for America’s thinly stretched defenses. In June 1942, the Navy began testing the Pelican, which used new “semi-active” radar homing technology. A year later, Western Electric upgraded the Pelican design with its “active radar” homing system.
Coupled with a 2,000-pound warhead, the upgraded Pelican achieved a 50% hit rate during tests at NAS New York. Additional tests and modifications followed, and the warhead was reduced to 1,000 pounds as the smaller explosive was shown to be sufficient for the expected types of targets. For a time, it seemed the Pelican would be the Navy’s production missile, but as the target types changed to surface vessels, the Pelican gave way to the Bat.
The ASM-N-2 Batwas a self-contained weapon system. While the Pelican required its mothership to continuously paint the target with a radar beam, the Bat’s onboard homing allowed much more flexibility with the launch aircraft. This early “fire and forget” system was considered a significant advantage in the face of enemy interceptors and AA fire.
Becoming the Bat
The Bat was a product of many fathers, with contributions by the National Bureau of Standards, assisted by the Navy’s Bureau of Ordnance, the Massachusetts Institute of Technology, and Bell Telephone Laboratories. While the Bureau of Standards developed the Bat’s aerodynamic and gyroscopic stabilizing systems, Bell Labs worked with MIT on the guidance mechanism.
The Navy’s Bureau of Ordnance said in its final review of the system:
“Bat was the product of many hands and minds. Of the groups working, Division 5 sponsored the Bureau of Standards organization, which built and tested the airframes and servomechanisms, the MIT Servomechanisms Laboratory, and the MIT Field Experimental Station. The results obtained can amply sustain credit for all concerned.”
Throughout the development process, radar systems were continually upgraded, and this demanded ongoing modifications to the Bat’s operating system. Advancing technology “moved the goal posts” several times, and the necessary modifications needed to make the Bat a workable weapon system, often seemed more of a setback than an enhancement. Plans were established to produce nearly 500 Bat bombs per month in the late summer of 1945—but at the end of 1944, the development team feared the war would be over before their brainchild could see service.
Consequently, development was refined enough to build 72 Bat glide bombs by the end of March 1945. Along with a cadre of experts, these were sent to the Naval Air Station at Kaneohe, Hawaii for training. The ASM-N-2 Bat (or SWOD, “Special Weapons Ordnance Device”,Mark 9 Modification 0) using an NBS airframe carrying a 1,000-pound AN-M65 GP bomb was readied for combat.
The Navy designated Number Two Wing, comprising squadrons VPB-109, VPB-123 and VPB-124, flying Consolidated PB4Y Privateer patrol bombers (the naval version of the B-24 bomber) as the initial Bat carriers. Other Navy aircraft were modified to carry the Bat, including the including the Vought F4U Corsair, the Curtiss SB2C Helldiver, and the Grumman TBF Avenger, but the PB4Y-2B Privateer was considered the best launch platform. The Privateer could carry one Bat under each wing in combat.
VPB-109 was sent to Hawaii to train with the new bombs, but only 10 days were provided to train the radar operators and ordnance teams. A few of the development team’s scientists accompanied the Privateer squadron to the PTO, helping to train the Bat operators and consult with the ordnance teams on assembly and maintenance.
The Bat Defined
The US Navy defined its radar-guided Bat in the following terms in its “Explosive Ordnance Manual”:
S.W.O.D. (Special Weapons Ordnance Device) Mk 9, or “Bat”, is a glide bomb. equipped with a radar homing set mounted in the nose. It is designed primarily for attacking. marine targets and is effective for night or day attacks upon shipping in any weather in which the parent plane can fly. The launching planes need not stay in the vicinity of the target and may release as many as four of these missiles in salvo.
The airframe consists of plywood sections which are fitted around the Bomb AN-M65. Control surfaces consist of an elevon on each wing which can be moved to control pitch or bank. There are no control surfaces on the tail.
In order to ensure destruction of the intelligence system the Demolition System Mk 122 is used.
Installation of the Fuses Mk 235 and Mk 236, with their outside windmills and flexible arming stems, is standard.
Control: This missile has its own radar transmitter and receiver. When the target is located on the scope of the monitor unit in the plane, it is put into the range step of the missile’s scope and is automatically kept there. At the correct instant, determined by a glide ratio scale, the missile is released and is guided to its target by the radar signal in its own scope. The guiding. radar supplies corrections to the servo system, which is also controlled by a gyro pilot, the device which maintains flight attitude
1,600-pound “Bat” S.W.O.D. Mk 9 (Air-to-Surface Missile)
Overall length 11.9 feet.
Wing span 10 feet
Total weight, 1,600 pounds.
Warhead: 1,000-pound GP bomb AN-M65
Fusing: Nose: Mk 235 Mod 0 Тail: Мk 236 Mod 0
Notes from the Bat Manual
I am certainly not a rocket scientist, so found portions of the wartime Bat operator’s manual to be helpful in describing some of the more technical aspects of weapon system.
Theory of Operation:
In SWOD Mk 9 Mod 0 the basic flight control of the air stabilizer is accomplished by two rate gyros (a pitch gyro and a turn gyro) which close and open contacts, operating the clutches of the servo. These air-driven gyros are powered by a Venturi tube projecting into the air stream.
A third gyro, designated “bias gyro”, sensitive to yaw motion only, is included in the gyro panel for the purpose of effecting a damping of yaw oscillations or hunting. A self-contained S-band radar transmitter and receiver is used to illuminate the selected target and to receive the returning echoes from it. The transmitter radar pulses from the antenna are directed by the rotating parabolic reflector so that the beam scans a cone-shaped area directly ahead of the missile. The returning target echoes are received by the same antenna, and the amplitude of the returning echoes varies with the directional pointing of the antenna beam. The returning target echoes are distributed by a commutator, mechanically coupled to the parabolic reflector, to four channels so that as the antenna beam is pointed down, right, up, or left, the returning echoes are segregated by quadrants. The echoes in each quadrant are converted by the directional control circuit of the radar into a direct current voltage which is proportional to the amplitude of the echoes of that quadrant.
The complete missile is suspended from the parent plane by means of a special bomb frame equipped with a standard bomb release unit such as Bomb Rack Mk 51 Mod 7. Sway braces are provided to keep the missile in a fixed position on the plane until release. The bomb fuses are mechanically armed after release by air vanes attached to the fuselage of the air stabilizer. Arming wires attached to the bomb rack release the air vanes at the time of drop-away in the conventional manner.
The Bat was considered breakthrough technology at the time, but even so it was fragile, sensitive, and sometimes downright wonky. The operator’s manual offers several “easier-said-than-done” tips for successful use:
“The parent plane should be straight and level for the last five seconds of the time that the SWOD Mk 9 is being readied for release. This permits the BAT to drop away normally on its glide path. The dropping aircraft should also be heading directly toward the target. Preferable air speed at the time of release is between 180 and 200 knots, with 140 knots as the minimum and 210 knots maximum.”
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Land attacks were particularly tricky, given that ground clutter easily confused the radar guidance system:
“Isolated target which gives a strong signal from 10 miles distance and is at least 2 miles from any equal or stronger signal.”
Meanwhile, overwater attacks were little easier, enemy ships rarely cooperated with adequate spacing.
“Target over water must be isolated by ½ mile from targets of equal or greater strength.”
Finally, the care and maintenance of the Bat demanded gentle handling and preferably a clean, dry, and temperate environment.
“It cannot be too strongly stressed that the SWOD Mk 6 Mod 1 (Gyroscopic assembly) contains gyro units which must be handled with as much care as normally would be given to a precision electrical meter. While units can withstand the mild shocks they will receive in transportation and normal use, they cannot be dropped or otherwise mistreated.”
The Bat in Action
As VPB-109 began operations on Palawan atoll during April 1945, the squadron soon found their greatest enemy wasn’t the Japanese, but rather the extreme environment of their Pacific island base. The sensitive mechanics of the new technology did not operate well within the extreme heat and high humidity.
Loaded onto the Privateers on the hot and sweaty Palawan runway, condensation soon formed inside the Bat’s radar brain when carried to their operational altitude (15,000 to 25,000 feet). Mechanical problems were common, and several Bats simply failed completely. Ground crews worked tirelessly to learn, adapt, and correct the problems.
The Bat’s first combat launch came on April 23, 1945, during VPB-109’s attack on Balikpapan harbor. Eight of the missiles were launched at a large Japanese freighter—and immediately half fell out as inoperable. The remaining four did not strike the designated target, their radar confused by the land mass clutter behind the target.
Even so, a small freighter was struck at the pier, a picket boat was hit while patrolling the harbor, and two Bats slammed into a nearby oil refinery. The first Bat strike was not a resounding success, but the crews and their new weapon had drawn blood, and the radar-guided missile concept was being proven.
The Navy Bureau of Ordnance commented on the early Bat missions:
“It was evident, even to the Japanese, that something was brewing when the squadron arrived on Palawan. The Bats had to be slung outside the carrying plane, one hung under each wing, and that was a tip-off. What was afoot turned out to be the first use of a completely automatic homing aerial bomb in combat.
At intervals from May until August 1945, a number of Bats were released experimentally against the enemy. As Japanese shipping was disorganized by that time, the only available targets were small ships, usually in or near harbors. In spite of the increased difficulty this situation presented to the operators, good hits were obtained. From distances of several miles, well beyond effective anti-aircraft fire, the Bats followed moving targets relentlessly until destruction was accomplished. The most spectacular of the hits occurred when an ammunition-laden picket boat vanished in one terrific blast and when a hapless destroyer had its bow blown off.”
By mid-May, VPB-109 moved to Okinawa. The conditions on Yontan Field were particularly soggy, and heavy rain greatly interrupted Bat operations. Also, the special tools, test instruments, and spare parts were lost when the squadron transport aircraft ditched in bad weather on the flight to Okinawa. Meanwhile, Japanese shipping was moving almost exclusively by night, and Privateers were forbidden to fly after dark to prevent being mistaken for Japanese night raiders.
Even so, VPB-109 made 13 Bat launches during its month on Okinawa—and three of these were hits. Privateer squadrons VPB 123 and VPB 124 joined the fight in July, and conducted several strikes on Japanese destroyers—with one direct hit recorded on a destroyer escort. VPB-109 launched the last Bat in combat on August 10, 1945, a near miss on a tanker off the coast of Korea.
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