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A full-bore (no sabot, but a pusher plate was used) cannon launched rocket. The stabilization fins would fold inward when in the cannon barrel, and flick out into position (as in the view in the photo) once the rocket left the cannon barrel. Since center burning rocket grains are desired (as opposed to end-burning), the rocket grain was supported during the cannon firing by filling the motor cavity with a liquid of similar density to the propellant grain. For this purpose a solution of zinc bromide solution was used.

This was a very capable little rocket (Martlet 3C, built by Lockheed Propulsion Corp.), serving as an excellent testbed for technology demonstrations. The volume between the missile and gun wall, as well as all other voids, was filled with dense liquid. Thus, while traveling in bore, the assembly was effectively a solid cylindrical column of uniform density.