The Remington 51 is a small pocket pistol

Pocket pistol

A pocket pistol is an American term for any small, pocket-sized semi-automatic pistol or, less-popular, any other handgun of small caliber, suitable for concealed carry in either a front or rear pocket of a pair of trousers, or in an exterior coat pocket...

 designed by John Pedersen and manufactured by Remington Arms

Remington Arms

Remington Arms Company, Inc. was founded in 1816 by Eliphalet Remington in Ilion, New York, as E. Remington and Sons. It is the oldest company in the United States which still makes its original product, and is the oldest continuously operating manufacturer in North America. It is the only U.S....

 in the early 20th century for the American

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 civilian market. Remington manufactured approximately 65,000 Model 51 pistols in .32 ACP

.32 ACP

.32 ACP , also known as the .32 Automatic is a pistol cartridge. It is a semi-rimmed, straight-walled cartridge developed by firearms designer John Browning, initially for use in the FN M1900 semi-automatic pistol...

 and .380 ACP

.380 ACP

The .380 ACP pistol cartridge is a rimless, straight-walled pistol cartridge developed by firearms designer John Browning. The cartridge headspaces on the mouth of the case. It was introduced in 1908 by Colt, and has been a popular self-defense cartridge ever since...

 calibers from 1918 to 1927, though small numbers were assembled into the mid-1930s.
John Pedersen designed or helped design many firearms for the Remington Arms Company.