Og and Nick,
The USN Seahawks had plumbing and floats installed in B and F model seahawks until the mid 90's. From the time I started they were plumbed for helium but, because there were no facilities on ships to carry helium, they were serviced with Nitrogen. End result? Inflation times varied from 30-70 seconds making them, essentially, useless (by the time they inflated, aircraft on descent rapidly in the ocean). There was a move in the early 90's to replumb the float system for Nitrogen (actually happened in some squadrons) but ultimately the decomissioned the whole lot because they felt it was a heavy burden to keep the systems serviceable in light of the very few aircraft saved by the system.
Thats the way I remember it (first hand).
Not much consolation to our Army brethren, but my two cents worth.
All the best gentlemen.
HP
Og...gidday!