It is both a type of sandwhich (everything edible available between 2 slices of bread) and a person who displays the characteristics of the newspaper comic strip hero of Dagwood & Blondie.  He is also the inventor of the Dagwood Sandwich. 

Sure is one hell of a military name ...........I first read it in 1960. Hasn't changed a bit. We British klnew it proved you Yanks were a bunch of mummy's boys. Blondie still is fruit though.

Big improvement on Andy Cap's wife.

OK JimBert

Got this out of Google

Callsign of the 16th Infantry Div WW1

Cheatingly yours (but good detective work)

Peter