Aircrews flying the Avenger soon found out that the forward-firing armament of one 7.62 millimeter Browning was entirely inadequate, lacking in range, hitting power, and volume of fire. Some Navy crews lashed up a 12.7 millimeter Browning on top of each wingroot as a fix; the factory came up with a better solution, mounting a single 12.7 millimeter Browning with 600 rounds in each wing, just outside of the propeller arc, resulting in the "TBF-1C". The machine gun in the cowling was eliminated and the gun trough faired over; the radio antenna mast was also moved back on the canopy a bit and set straight upright, instead of being slightly angled as it was in the TBF-1, and provision was added for a drop tank under each wing.
    The TBF-1C entered production in the summer of 1943; Eastern built it as the "TBM-1C". The enhanced armament proved particularly useful in suppressing defensive fire on naval targets. The TBF-1C was the last version of the Avenger actually manufactured by Grumman, with 764 built; in late 1943, Eastern took up all Avenger production so Grumman could focus on the F6F Hellcat. Sources also mention various minor subvariants of the TBF-1/1C Avenger, such as:

    * "TBF-1P" and "TBF-1CP reconnaissance versions of the TBF-1 and TBF-1C respectively.

    * The "TBF-1E", which was a special electronics platform, possibly for electronics warfare.

    * The "TBF-1J", fitted for arctic operations.

    * The "TBF-1L", with a searchlight in the bombbay.

    There were comparable subvariants of the TBM-1/1C as well -- "TBM-1P", "TBM-1CP", "TBM-1E", "TBM-1J", and "TBM-1L". Details and quantities of these machines are hard to find. 334 TBM-1Cs were provided to the Royal Navy FAA as the "Tarpon II"; some sources identify the Tarpon II as the TBM-1, but this appears to be an error. A total of 48 TBF-1/1Cs was also provided to the Royal New Zealand Air Force in 1943, with these aircraft seeing considerable action against the Japanese. No other combatants used the Avenger during World War II.

    * Although the heavier gun armament of the TBF-1C was welcome, Avenger crews remained frustrated by the fact that the standard Mark 13 air-dropped torpedo was finicky, requiring a careful drop at low speed and altitude, and even then it often malfunctioned. The whole story of the US Navy and torpedoes during World War II is a sorry one: overall, torpedoes were among the most notoriously troublesome gear supplied to the US Navy during the war, and it took a lot of painful effort just to get them up to the level of mediocre.

    The Mark 13 did end up receiving a number of improvements, initially a stopgap fix involving a plywood box built around the tailfins that improved stability during drop and broke away on hitting the water. The ultimate solution was a ring tail developed by the California Institute of Technology (CalTech) that was welded onto the pre-existing tailfins. The resulting Mark 13-1A torpedo was much more satisfactory, able to be dropped from reasonable altitudes at high speeds. However, while work on the fix progressed, Avenger crews became more proficient at glide and skip bombing, with an Avenger diving in at a moderate angle and then dropping a string of four 225 kilogram (500 pound) bombs that skipped into the hull of the target, detonating with a delayed-action fuze. In the end the Avenger, built primarily as a torpedo bomber, would drop far more bombs than torpedoes.

    * In the meantime, the Avenger was proving useful in fighting the U-boat menace in the Atlantic. The balance of power between German submarines and Allied sub-hunters had been shifting back and forth through the war; in early 1943, it seemed like the U-boats were getting the upper hand again. However, the Allies were introducing improved tactics as well, such as codebreaking, radio direction finding networks, improved radars, and long-range shore-based patrol aircraft. One particular enhancement was the introduction of small escort or "jeep" carriers, designated "CVEs", that provided air support, generally with Wildcats and Avengers, to convoys or free-ranging "hunter-killer" groups.

    For antisubmarine warfare, many Avengers were refitted with microwave ASD radar in a pod mounted on the right wing. The ASD was a big improvement over the longwave ASB, providing greater discrimination, though at least in some cases the ASB was retained since it provided better long-range search; the ASB's Yagi antennas were relocated to the top of the wing. Avengers refitted with the ASD were redesignated "TBF-1D" and "TBM-1D". The radome affected low-speed handling a bit, but it wasn't regarded as seriously troublesome. One Avenger was experimentally fitted with the radome on top of the cockpit, presumably to eliminate the drag asymmetry, but the configuration wasn't adopted, possibly because it wasn't very healthy for the pilot.

    In some cases, ASD-equipped Avengers were stripped down, fitted with flame dampers on the exhausts and additional fuel tanks, and sent aloft at night to try to spot U-boats lurking on the surface in the darkness. These "Night Owl" Avengers were not armed and had to call in attack elements to perform a kill, providing illumination using parachute flares.

    Antisub Avengers were usually armed with 160 kilogram (350 pound) depth charges, set to go off at shallow depth, ensuring that even a miss on a U-boat cruising on the surface was likely to be fatal. The FAA also introduced the use of unguided rockets, fitting four launch rails for British 8.9 centimeter (3.5 inch) rockets under each wing. The rockets could be fitted with bulbous explosive heads or solid penetrating heads; the penetrating heads were more appropriate for attacks on U-boats and other naval targets.

    A number of US Navy Avengers were also fitted for carriage of the rockets, but by early 1944 Avengers were carrying the more formidable 12.7 centimeter (5 inch) "high velocity air rocket (HVAR)" or "Holy Moses", developed by Caltech. Eight HVARs were carried, using new twin-stub launchers that were much more aerodynamically clean than the cluttered launch rails used for the British rockets. The rockets gave an Avenger one hell of a punch, and were also heavily used for ground attack. Late in the war, Avengers obtained the Mark 24 acoustic homing torpedo, which would home in on the sound of a submarine's propeller.

    In midwar, US Navy Avenger colors changed to dark blue on top, medium blue on the sides, and white underneath for Pacific-based aircraft; while Atlantic-based aircraft had medium blue on top and medium gull gray along the sides and on the belly. From October 1944, all US Navy Avengers were painted overall dark blue.
    Regards Duggy.

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