M-69 incendiary

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The M-69 incendiary cluster bomb was used to target Japanese cities during World War II. They were nicknamed 'Tokyo Calling Cards'.[1] The M-69 was a plain steel pipe with a hexagonal cross section 3 inches (7.6 cm) in diameter and 20 inches (51 cm) long. It weighed about 6 pounds (2.7 kg).[2]

The bomb used napalm (jelled gasoline) as an incendiary filler, improving on earlier designs which used thermite or magnesium fillers that burnt more intensely but were less energy/weight effective and easier to put out.[3] In Germany they were filled with jellied oil and dropped in clusters of 36 in the non-aerodynamic M-19 bomb.[4] Over Japan they were used in clusters of 38 as part of the finned E-46 'aimable cluster', which opened up at about 2,000 ft (610 m). After separation, each of the 38 M-69s would release a 3-foot (1 m) cotton streamer to orient its fuze downward.[5][6] Upon hitting a building or the ground, the timing fuze burned for 3–5 seconds and then a white phosphorus charge ignited and propelled the incendiary filling up to 100 feet (30 m) in several flaming globs, instantly starting multiple intense fires.[2]

It was tested against typical German and Japanese residential structures at Japanese Village and German Village, constructed at Dugway Proving Ground, Utah, in 1943.[7] The M-69 was the most successful incendiary in the tests.[2]

Against Japan, the M-69 was carried in the bomb bay of the Boeing B-29 Superfortress, with a typical load containing 40 cluster bombs, a total of 1520 M-69 bomblets.[2] The bombs were very effective in setting fire to Japanese cities in mass firebombing raids starting in February 1945 against Kobe.[8] In the first ten days of March 1945, raids with the M-69 and M-47,[9] extensive damage was done to Tokyo, Nagoya, Osaka, and Kobe.[10]

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