Renown is not a shop or script where you buy anything. Bdu gave their best boats and crews to those who 'earned' the right and respect based on their experience and tonnage and by following orders. The Bdu had limited assets and obviously those assets went to the very best!
So, again unless I am wrong, one 'earns' their way up the ladder with 'renown'.
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DID, no cheats, no shortcuts, no non-historic equipment deviations. Boat and crew safety is integral with my immersion style! Follow the historic events during your patrol:
http://www.uboat.net/today.html