User blog comment:Admiral Mikado/Extra Operations for Dummies: 1-5/@comment-200.95.15.19-20160307234645/@comment-28234298-20160424230025

Nope, it just depends on your the sub you want really. I got my first sub with my HQ lvl 36 (I-58). So subs like I-58 and I-168 drop at any lvl HQ but some other subs require level 40 to 80 for them to drop. (I-19 and I-8). ofc you can also craft them :v