Actually, I believe it is a 99K which is 3/4 size of the 99. I agree with the bonus of being a hand crank. Early machines were either a hand crank or treadle. Later the options included a motor version. From what I can make out of the serial number it looks like the serial number was allocated June 11, 1937.
https://ismacs.net/singer_sewing_mac...l-numbers.html If you notice the decals kind of go over the bump leading to the nose of the machine. Here is another site that has lots of other Singer machines, but look for hammerhead and notice it is for 99.
http://vssmb.blogspot.com/2011/08/vi...ingers_16.html
The only Class 99k with hand crank was 99K2 listed at
https://ismacs.net/singer_sewing_mac...sses-1-99.html but it has small tension discs. I looked at some other parts manuals and there are hand cranks for some of the other 99Ks. I couldn't find a parts list for 99K2.
Have fun with it.
ETA - The K after the 99 just means that it was made at the Kilbowie plant in Scotland.