basically any soft skin of course, but essentially any armored car or halftrack was dead meat, virtually any Japanese armor, Japanese destroyers or lighter ships were definitely able to be penetrated in many areas
in the ETO destroyers were better armored, tanks especially older models such as the panzer 3 and its variants, Panzer 1&2s,
on newer/heavier units such as panzer 4s, panthers and tigers, from most angles they were immune except for vision block hits and such, from higher angles such as strafing aircraft, engine decks, ventilation areas, external fuel and such were able to be damaged
now there are pilots who swear they were able to take out tanks by hitting the bellies, and there are films showing rounds bouncing off foads into tanks, but i have never heard of any after action report listing belly damage from 50 sized weapons