I think the history is slightly different than given in above post.
"Hammer Brand" was a branding used by New York Knife Co. from 1878 until their closing in 1931. These were very well made knives, some of the best ever manufactured in USA.
In 1936-37 Imperial Knife Co. acquired the Hammer Brand name and used it on many of their knives up until 1955.
In 1947 Imperial, Schrade-Walden and Ulster developed an association with each other presumably to cooperate rather than compete. It was in 1984 that the Baer brothers who owned Schrade and by then Ulster as well, purchased Imperial to become "Imperial Schrade Co." which operated until 2004.
Your knife is from 1937-55. There were 3 different stampings for these in which the arm in the logo is slightly different. If a tang stamping is well struck and well preserved, then these differences in the arm can be used to further date the knife within the 1937-55 time period.
Having said all this, there is always some debate around the exact history of knife companies so my understanding of it could be 'off' and further correction made by those who specialize in knife history.
If "Codger" reads this, he is the expert on the history of these knife companies.
kj