Playing only training missions, but takes near to forever to reach LVL 120, another way is stay away from action.

But, basicaly, sailors have to die sometime.

Pull the plug by accident on purpose.

thanks, very helpful tips...

How much casualties you have in average? Are you playing CV or BB?

If sailors would not die, SDE could not make money by selling Olives that buy Experts and Veterans. The death is part of business model, you see. 

Few years ago Medic was very useful (after lvl 95ish).  The price for Medics was high but now they say Medic does not work properly. Which is strange, given that Ability exists, unlike the Accountant or Drill Instructors which were designed but never implemented.  

Want to avoid crew death? Add some bulk head to your ship.

DC misteriously after you've gotten your officers killed.

Do not know, what situation does cause your crew death, but about BBs being critical hit (especially from high angle japanesse guns):

1/ Believe armor helps, i have read some threads about it and my experiences confirm this statement. Important is to have "citadel" armored = belt and deck in the same time. So add 0,2-0,4 for the belt and deck (recommend 0,4). 

2/ Also high lvl Seaman (above 95-100) seems helps. 

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Would say that each precaution can half the number of deaths.  (Never regulary tested, but after hundreds of battles doing so...): 

 - Without armor and Seaman even 15 sailors can be lost in the moment  when full high angle salvo land on the ship (e.g. Andrea Doria).

- Now 1 sailor (or 2) once per 3 lost battles, rarely 4 (once per 10 lost battles) die. Sometimes one of those 4 is expert. Believe no veteran died when armor+seaman were implemented (without armor+seaman, veterans die sometimes). Playing KM ships. 

Hope it will help you also.

Don't install NFfixer
Do not under any circumstances tamper with it or change its options.
And do not press ctrl + del at any point of the game. 

Can you us a US medic?