[ghaff]

That claim gets made but there's nothing in the actual novel to actually support it, e.g. "A term of service isn’t a kiddie camp; it’s either real military service, rough and dangerous even in peacetime . . . or a most unreasonable facsimile thereof. Not a vacation. Not a romantic adventure. Well?" He then goes on to talk about things like "field-test survival equipment on Titan" as an alternative. (It's also explicitly mentioned that the merchant marine isn't included.)

[dragonwriter]

The merchant marine isn't civil service, now, either; to quote Heinlein's own response on this:

In Starship Troopers it is stated flatly and more than once that nineteen out of twenty veterans are not military veterans. Instead, 95% of voters are what we call today "former members of teh federal civil service."