Looking at my best reference book for the Gilberts
"The US Army in WW2" "Seizure of the Gilberts and Marshalls" These are genuine Army volumes with specific photos of the operations. I see a few carbines being used by Marines and Army personnel. No bayonet lugs and no adjustable sights indicated. This book covers the taking of Makin, Eniwetok, Kwajalein, Tarawa (Betio) and lesser islands. Later operations such as Iwo Jima, appear to show a much larger percentage of carbines.
6th Marine: I had a late friend who spent 36 months
in the South Pacific in the Marine Corps. He told me that he shot a Japanese six times with a carbine before he finally went down. This was on Guadalcanal. He obviously had his islands mixed up since he would have had a Reising, 03, BAR or maybe a stolen Army Garand, no carbines yet. I might not be surprised if an adjustable sight showed up on Iwo Jima or Okinawa, but in 1943 in the Gilberts/Marshalls would be a real stretch. These guys aren't lying or even stretching the truth, they just get the time and place mixed up, God bless them.