▁conduct ▁reconna issance ▁operations , ▁first ▁at ▁Well ington ▁and ▁A uck land ▁in ▁New ▁Zealand , ▁and ▁then ▁at ▁Su va ▁in ▁F iji . ▁ ▁Between ▁ 1 ▁and ▁ 2 5 ▁June , ▁when ▁the ▁four ▁sub mar ines ▁arrived ▁at ▁K w aj ale in ▁At oll ▁in ▁the ▁Marshall ▁Islands ▁to ▁re - supp ly ▁before ▁proceed ing ▁to ▁Japanese ▁ship y ards ▁for ▁maintenance , ▁the ▁four ▁sub mar ines ▁attacked ▁at ▁least ▁seven ▁Al lied ▁merchant ▁vessels . ▁Three ▁of ▁these ▁were ▁s unk : ▁Iron ▁Ch ie ft ain ▁by ▁I - 2 4 ▁on ▁ 3 ▁June , ▁Iron ▁Crown ▁by ▁I - 2 7 ▁on ▁ 4 ▁June , ▁and ▁Gu atem ala ▁by ▁I - 2 1 ▁on ▁ 1 2 ▁June . ▁The ▁first ▁two ▁attacks ▁resulted ▁in ▁ 1 2 ▁and ▁ 3 7 ▁fatal ities ▁respectively , ▁though ▁the ▁third ▁attack ▁killed ▁no ▁one . ▁The ▁attacks ▁forced ▁the ▁authorities ▁to ▁inst itute ▁changes ▁in ▁merchant ▁traffic ; ▁travel ▁north ▁of ▁Melbourne ▁was ▁restricted ▁until ▁a ▁system ▁of ▁esc orted ▁con vo ys ▁was ▁established . I - 2 1 ▁was ▁the ▁only ▁sub marine ▁to ▁return ▁to ▁Australian ▁waters , ▁where ▁she ▁s ank ▁three ▁ships ▁and ▁dam aged ▁two ▁others ▁during ▁January ▁and ▁February ▁ 1 9 4 3 . ▁During ▁her ▁two ▁deploy ments , ▁I - 2 1 ▁s ank ▁ ▁of ▁Al lied ▁sh ipping , ▁which ▁made ▁her ▁the ▁most ▁successful ▁Japanese ▁sub