This pen has a "military" clip. The Army uniform regulations at that time required the breast shirt pocket flap to close without any protrusions or bumps. Most of the pens makers devised models whose clips reached the top of the cap so the pen would be entirely inside the pocket when clipped to the top edge. Apart from this distinctive cap, the pen is the same as a Balance Sovereign.
The US was in wartime production mode so brass was restricted. Sheaffer used silver as the base metal for the clip and cap bands. Gold plated sterling silver is generally called vermeil. Sheaffer did not mention the use of silver in their 1941 catalog so it seems reasonable to assume the silver is not sterling. The clip end and cap band have severe plating loss but I think the silver shining through looks great and it provides opportunity for the pen to tell a unique story.
This is a Vacuum-Fil which is like a Visconti power filler or a twsbi vacuum filler. The filler restoration is guaranteed for at least one year provided Noodler's ink is strictly avoided. It is notorious for staining celluloid and melting rubber filler parts.
The nib is a narrow LIFETIME. It is narrower than the nib on the top-line Balance Premier (Oversize). I believe it to be a nicer nib because it's narrow profile provides some very slight softness compared to the notoriously rigid Premier nibs. The fine nib is equivalent to a modern, western extra-fine or a Japanese fine.