This photo is a detail from a post card sent in September of 1917.
As I read it, it says,
Hello Doc. Walt and I are now regular sailors except that we have never been on the water and don't know how to sail. Write. Jack.
[Corrected the typo "Walt and I are now..." is correct, not "Walt and I are not...." I made that same error a few years ago on a newsletter and got raked over the coals but my fingers still make the same error at times and the spell check just doesn't catch it.]