[PatG]

You will get kills with the 57mm at 0 hex range. The 37mm inf gun - a copy of the French puteaux has relatively good AP performance (as in only in this theatre at this time period and compared against what else is available). AT work is pretty much down to your Gunjin. Suppress the hell out of the target with knee mortars then move in for close assault. Luckily, you recover from suppression very quickly. Engineers would be another option.

In a previous campaign, I have had Chinese and Japanese armour bypass each other because their main guns could only scratch each others paint!

Watch out for 37mm panzerknackers in Nationalist Chinese service they can really chew you up. The Japanese get a copy of this and all around better ATG in the late 30's.