 
 <prompt> Wetin be di biggest caliber for mm wey US Army don use? Based on di question wey dey before, write small tori wey get di answer. E fit be 1 - 20 sentences. Context: <response>: After World War I, US Army start to dey develop dual-role (AA/ground) automatic 37 mm cannon, wey John M. Browning design. Dem standardize am for 1927 as T9 AA cannon, but trials show say e no dey useful for ground role. Even though the shell dey light small (well under 2 lbs), e get good effective ceiling and dey fire 125 rounds per minute; dem come develop AA carriage for am and e enter service for 1939. The Browning 37mm dey always dey jam, so dem come replace am for AA units with Bofors 40 mm. US Navy bin dey eye Bofors since, but dem no buy any until 1939. Also, for 1931 US Army work on mobile anti-aircraft machine mount for back of heavy truck wey get four .30 caliber water-cooled machine guns and optical director. E no work well so dem abandon am. 