On the first of this month, Okinawa was invaded by the US Army, Navy, Air Force, and Marines.
See menu items “SOME HISTORY” -> “The Battle of Okinawa”
African-American US Marines and sailors resting at the base of a Japanese war memorial, Okinawa, Japan, 12 Apr 1945. On steps: Snowden, Martin. On monument: Walton, Ellenberg, Brown, Brawner. ww2dbase
“My first lesson in soldiering came from a GI named Slim. He showed me the best available fox hole, and how to lie flat when bombs drop, arms folded under to avoid concussion. He told me my helmet and gun were my best friends. The former is used to protect the head and face; for washing and taking a bath; and when stuck in a fox hole under fire for certain unmentionable but very necessary activities. It’s a swell gadget. Artillery at the front sometimes roars all night; it shakes the ground and hurts your ears.”
“Have been very very busy days and every evening. About the time I set up a Coleman lantern and start to write something, the Nips come over and raise a bit of hell with us. Am getting damn tired of spending most of the night sitting in a dugout.. but c’est la guerre or however you spell it.”
More from the Okinawa battle: in this April 20 letter Grandpa Knowlton writes about a rocky ridge running through Okinawa that the soldiers called “Tombstone Ridge”. This was not the ridge from the Hollywood film: “Hacksaw Ridge”. See https://history.army.mil/books/wwii/okinawa/chapter8.htm
April 23, handwritten, 4 pages
“The other night a Jap zero fell 20 paces behind one of our warehouses, and the boys inside were asleep. Some mess… it was in a million pieces as was the Jap. A medical colonel sitting nearby was uninjured, although blown 100 feet through the air. Whatta war.
The night raids are very spectacular. Our ack—ack looks like hundreds of Roman candles, and the colors are beautiful, orange and white. When they get a bomber in several search lights and then bring him down it’s a real thrill; but in the meantime we hear the dull thump thump as he drops his eggs, its a nasty feeling.”
Unlike the Naha chapel, 
the shrine in a cave, as Grandpa Knowlton mentions in the April 30 letter, was used as an air-raid shelter in 1945 and did not get damaged during the Okinawa battle.