As the invasion flotilla hove to in the predawn hours, the island's four 8-inch guns opened fire. A gunnery duel soon developed as the main batteries on the battleships "Colorado" and "Maryland" commenced counter-battery fire. This proved accurate, with several of the 16-inch shells finding their marks. One shell penetrated the ammunition storage for one of the guns, setting off a huge explosion as the ordnance went up in a massive fireball. Three of the four guns were knocked out in short order. One continued its intermittent, though inaccurate, fire through the second day. The damage to the big guns left the approach to the lagoon open.