You have a pre-Victory model S&W M&P revolver made for the British during WWII. Yours would likely date from early 1941. You do not provide a picture. However, the originals normally had a 5" barrel length (measured from the front face of the cylinder), and a blued finish. Unfortunately, the modified chambers destroy any collector value, but it could be a good shooter. It is safe to fire .38 Special ammunition, but the cases will bulge as the chamber diameter is oversize.