In WW1 heavy trench coats were usually worn by everybody.They werent always easy to penetrate with an edged weapon,thats why the triangle blade,it punched through a lot easier.The A.C.co version is rarer than the LF&C version.Do you have the scabbard?Hope so,if not its worth a little less.My guess is its worth around 500 bucks give or take.Dont clean it to much or take any rust off of it with a wire brush or anything.you dont want to hurt the blued finish.
No scabbard ! I won't clean it either , it's in pretty good shape! I'll just sit on it for awhile and hope it goes through the roof someday in price!
Make sure it is authentic! Two WWI L.F.&C U.S. Model 1917 Trench Knives WWI Trench Knife - A.C. CO. USA 1917