This has been discussed in other threads, the early retirment seems to be linked to being given command of a Balao Sub before they were actually available, therefore when you return to base after your first patrol in the Balao you get forced retirement.
Fix - When asked if you want to upgrade your sub, select no. Just wait for the Sub upgrade to be offered again later in the campaign.
I have tried this and it works
And just one other thing, please stop using text speak in this forum, it is really annoying and does not help in putting your point accross
