Cool pic! I don't think there were M1icon helmets in Bataan. Garands yes, but not M1 helmets. If I were to guess, this photo was taken in Guadalcanal. I remember in the book Helmet For My Pillow by Robert Leckie, he mentioned seeing newly arrived army units that still wore the old Kelly helmets.

As for the mentions of the 26th Cavalry, they were the first ones to use the Garand in ground combat in WW2 when they met the Japaneseicon landing at Lingayen Gulf. The US Army infantry and cavalry units were issued garands in 1941 before war broke out.