Further info:
The gun is made on S&Ws medium sized round butt 'K frame', aftermarket grips should fit if you wish to shoot it without damaging the pearl grips.
S&W used true mother of pearl for its factory special order grips, if they are from S*W ther should be a) a S&W logo medallion inset into the grips and b) the serial number of the gun should be penciled on the inside of the left grip.
Value is quite variable, from around $150 in fair condition to $650 in excellent plus (almost new). If unfired with box it could be as high as $1600. Decent pics would be needed to give an evaluation.
U.S. Service CTG refers to the .38 Long Colt Cartridge, which was the issue cartridge for the US military at the time. S&W were not going to stamp Colt on one of their guns. The .38 S&W Special is a stretched version of the .38 Long Colt, so both rounds can safely be chambered and fired.
This gun predates heat treatment of cylinders and should only be fired with standard pressure lead ammo. No PlusP or +P+ marked increased pressure loads, nor should jacketed or semi jacketed ammo be used. These tend to have higher or longer peak pressures.
It also predates the internal hammer block safety. If dropped it could fire. So treat it as a five shooter and leave the chamber under the hammer empty.