At the height of the daytime air war over Europe. American airmen deaths dwarfed Iwo Jimas entire USMC losses. They were staggering - sometimes thousands per month.
The Marines lost 6800 dead in 36 days, I am aware of the US losses during the air campaign in WWII, 30000 dead in 994 days of combat operations in Europe. The dead from Iwo were 2% of the total American dead from the war.
The Imperial Japanese Army positions on the island were heavily fortified, with a vast network of bunkers, hidden artillery, and 18 km (11 mi) of underground tunnels. The Americans were covered by extensive naval and air support, capable of delivering an enormous amount of firepower onto the Japanese positions. The battle was the first American attack on the Japanese Home Islands, and the Imperial soldiers defended their positions tenaciously. Iwo Jima was also the only U.S. Marine battle where the American overall casualties exceeded the Japanese, although Japanese combat deaths numbered 3 times that of Americans.
Of the 22,000 Japanese soldiers present at the beginning of the battle, only 216 were taken prisoner. The rest were killed or missing and assumed dead. Despite heavy fighting and casualties on both sides, Japanese defeat was assured from the start. The Americans possessed an overwhelming superiority in arms and numbers; this, coupled with the impossibility of Japanese retreat or reinforcement, ensured that there was no plausible scenario in which the U.S. could have lost the battle.
US casualties: 6,821 killed/missing; 19,217 wounded.
During this one-month-long battle, 27 U.S. military personnel were awarded the Medal of Honor for their actions, 13 of them posthumously. Of the 27 medals awarded for the actions at Iwo Jima, 22 were presented to Marines and five were presented to United States Navy sailors; this was 28% of the 82 Medals of Honor awarded to Marines in the entirety of World War II.