Gambit

Gambit is a 1973 game by David W. Currie, published at Challenge Games.

The game is played on the following 10x16 board:

The game has a Chess-like feel, with four types of pieces representing military vehicles, and three types of positions (!) representing land, sea and air. Winning can be done either by elimination or reaching the opponent's home position. There is a collection of interesting moves made possible by combining pieces.

These are the original rules:

note: the first page shows the initial setup with 19 pieces per player. However, the game came with only 18 pieces. There is an amphibian piece at the top-right corner, in the setup diagram, that is a misprint (correction mentioned by Patrick Kelley).

 

big thanks to Patrick Kelley for sharing these rules 

There's a comment on BGG's page regarding Gambit's board and cover:

The map for at least one printing is a bit of a curiosity. In it, the cover of the box shows a 10x10 board with alternating green and blue squares. The instructions note that the land squares are green and the sea squares are blue. However, the actual map provided is 10x16, has only black and white print on yellow paper, and uses the letters "L" and "S" to designate land and sea spaces. It would appear that the designer assumed he would be able to print color boards, but then had to fall back to a simpler black and white drawing printed on yellow paper.