I second the recommendation for ‘War Bush’: one of the best divisional histories from the campaign (which also includes the history of the 3rd West African LRP (‘Chindit’) Brigade) and a long-overdue counterbalance against the shameful treatment of the West Africans in Kirby’s official history.
Don’t forget that in addition to 81st West African Division, there was also 82nd West African Division, 11th East African Division, two independent East African Brigades and numerous African ancilliary units such as West African Heavy Anti-Aircraft Regiments, which engaged Japanese air attacks against India.
Re Japanese AT grenades: One of the regimental histories (3rd Carabiners?) recounts the tale of a tank commander being attacked by ‘Thai’ troops (probably actually just Japanese of large stature) throwing glass phials at his tank. He noticed a strange smell, looked down and noticed that his crew had all passed out (they soon made a complete recovery). The history goes on to say that these were phials of Hydrocyanic Acid. A Japanese account recounted in Lyall-Grant and Tamayama’s excellent ‘Burma 1942’ recounts a Japanese order to deploy ‘special gas grenades’ against the Stuarts of 7th Armoured Brigade.
Re the direct fire big gun: Each Indian Corps (IV, XV and XXXIII) formed an AGRA (Army Group Royal Artillery), which comprised various artillery units, but at the core of each was a Medium Regiment of 4.5 or 5.5 inch BL Guns and a Heavy Anti Aircraft Regiment with QF 3.7 inch AA Guns. These were often used over open sights against hilltop positions. I’ve seen a photo of a pair of 3.7s being used like this and one of a ‘sawnoff’ 5.5 being used against Japanese positions on the top of Kennedy Peak, southeast of Imphal. Another sawnoff 5.5 was also used ‘Napoleonic style’ to create a breach in the massive walls of Fort Dufferin in Mandalay.