Hamish,

"Leatherneck" is the nickname for the US Marine Corps. It comes from the early 19th century, when the marines (and for that matter, other branches of the forces) wore high leather neck stocks to prevent sword blows to the neck. The "Leatherneck" tartan is named for this.

There is a US Marine Corps Association Pipe Band that wears a solid blue kilt as you described -- see:

http://www.leatherneckpipeband.com/

and

http://www.marinepipers.com/

There is a nice story from the USMC magazine about piping in the Marines on the second site.

Also, Don McKee's site has some USMC cap badges for bonnets and belt buckles:

http://www.scottishregalia.com/


I believe the Scottish Lion has Leatherneck tartan:

http://www.scottishlion.com

Cheers,

T.