> Total U.S. military deaths in battle and from other causes were 407,316. The breakout by service is as follows: Army 318,274 (234,874 battle, 83,400 nonbattle),[292] Navy 62,614,[292] Marine Corps 24,511,[292] and the Coast Guard 1,917.[570][320]
I don't know what the denominator looks like for those various forces, but 5x as many Army deaths as Navy seems to corroborate your grandfather's intuition.
[1] https://en.wikipedia.org/wiki/World_War_II_casualties#endnot...
Edit: From [2] it seems the Army was a bit over 2x the size of the Navy, so still about 2x the rate of deaths.
[2] https://warfarehistorynetwork.com/us-involvement-in-wwii-how...
The Battle of Leyte Gulf was the biggest naval battle in history. If he was in the pacific I am sure he seen some crazy things.