It is a U.S. Navy Survival Knife, usually called the "Giant Jackknife" for obvious reasons.
6" long when closed, 15 5/8" when both the blade & saw are opened.
They were made by Colonial Prov. RI, and by United, in Grand Rapids Mich.
They were issued in an O.D. Green canvas pouch that fit a pocket in the survival vest.
Issued during WWII to both Navy & Army Air Force pilots.
Many were sold as surplus by United Machine Tool after WWII ended for $2.95 ea, and the ads said 60,000 United brand were used in survival kits.
Many you find now have the saw blade broken off, as they were allowed to use scarce 16% Tungsten steel for the saws, and it is very brittle. At that time the war department had issued a ban on using any Tungsten steel with more then 6.75% for any weapons production but the Giant Jackknife had a "life-saving" role so an exemption was made for them..
The knives were first issued in 1944 and were last used in the early 60's when the fixed blade Jet Pilots Knife was adopted service wide.
rc