The Marines attempted another drive into Belleau Wood, this time with the 1st Battalion, 6th Marines. They gained some ground, but soon were brought to a halt by heavy machine-gun fire plus large amounts of German mustard gas. The losses were already the heaviest in the history of the Marine Corps, and the end was not in sight.
Operation Gneisenau continued, but the second day was not as successful as the first day had been. French artillery took a heavy toll of the advancing German infantry. Also on this day, General Jean Degoutte took over command of the French Sixth Army. This may or may not have helped the French defense immediately, but Degoutte appears to have been a superior commander to General Denis Duchêne.

The Austrian navy was being hampered from attacking Allied shipping in the Mediterranean by Allied ship patrols and mines at the Straits of Otranto. Attempting to break through, the battleships SMS Szent István and her sister ship SMS Tegetthoff, plus seven other ships, set sail in the early hours of the morning to attack. But the Italians were awake as well, and at 0330, the Szent István was hit by two torpedoes from the motor torpedo boat MAS-15. They struck the boiler rooms, and one by one the boiler fires were extinguished by the incoming water. Eventually the Szent István lost too much power to run the pumps, and she capsized and went down.
There happened to be a movie camera on board the Tegetthoff, and for the first time, the sinking of a battleship was captured on movie film. Note the Szent István and her sisters were among the world's earliest battleship designs to mount triple main gun turrets. (The footage has occasionally been mistaken for WWII footage.)
https://www.youtube.com/watch?v=5pSiCjfhUUw