If American and British land on homeland of Japan, that casualties must unimaginable! Accoding the estimate of US, 1 million soldiers will die and wounded in the invasion. Due to nearly 5 million militia mobilised in Japanese homeland. Even though these troops were new formation! Many of them lack of guns and cannon.
But I think it still serious threat to US and British. First reason, always have soldiers perish in the battle! you don't need equip one soldier one gun.In theory, 10000 Japanese soldiers equip 5000 rifles that is enough! A soldier die at conflict! another Japanese soldier will receive his rifle and continue shoot! Because the air strike! The steel producition of Japanese until 1945 August only 1/4 compare 1944, only 0.98 million tons.but that is enough. Because most of steels ,the Japs use built navy and ships. compare the land force consume steels were less.
0.98 million tons steel.If Japanese built tanks(consume steel much more than artillery) less comparative. It can manufacture millions rifles, tens of thousands 75- 150 mm cannons and mortars.