Origin of 'hit the sack'?

I know it means to go to sleep but where did it originate from. I'm looking for first use. Just curious.

Solution 1:

Mattresses used to be stuffed full of hay, or were sacks full of hay. Thats why we say "hit the hay" or "hit the sack."

Solution 2:

In the entry for sack on the Online Etymology Dictionary:

Slang meaning "bunk, bed" is from 1825, originally nautical. The verb meaning "go to bed" is recorded from 1946.

Solution 3:

The OED has it from 1943 in James J. Fahey's Pacific War Diary, 1942-1945:

I hit the sack at 8 P.M. I slept under the stars on a steel ammunition box two feet wide.

It's in the same entry as the earlier hit the hay, from 1912 in Dialect Notes:

Hit the hay, to go to bed.