It's just an attempt at realism, since most captains didn't patrol forever. There are some others, which I've only read about since I've never played long enough to get that deep into a career.
The SH3 Commander User Guide explains this. Once a Kaleun is retired you can continue the same boat's career with a new captain.
Another option is, when starting a new career, go to the Career Options panel and make sure that Simulate a Realistic Career Length is unchecked.
__________________
“Never do anything you can't take back.”
—Rocky Russo
|