Civilians proved to be a major problem for the Americans during the Battle of Okinawa; roughly 300,000 still remained on the island by 1 April 1945 when the invasion was launched.

Civilians became a nuisance to combat units after the assault on the final enemy lines began, and remained a burden until front lines no longer existed. More than 10,000 civilians stayed on Chinen Peninsula and were relatively unharmed by the battle. A much larger number, forced south by the advancing lines, hid in caves or stone huts until they were overtaken. Then they tried to pass through the machine-gun and shell fire to enter American lines or attempted...slipping through the front lines during darkness. Infantrymen helped...as much as possible and often interrupted the fighting to collect and guide them through the front lines. During the last days of the fighting there were always groups of civilians sitting just behind the front lines, waiting for help, instructions, or, as many of them believed, death.

Eighty thousand Okinawa[n] civilians, between a third and a half of whom were wounded, crawled from caves at the south tip of the island during the last two weeks of June. These were either children, the very old, or women; there were few able-bodied men among them. In long columns they walked toward the rear. Most of the women carried babies on their backs and bundles of clothing, food, dishes, and kettles on their heads--all they owned....The bodies of many thousands of other civilians lay scattered in the ditches, in the cane fields, and in the rubble of the villages, or were sealed in caves.

A large number of Okinawan civilians, mostly men from the ages of fifteen to forty-five, were formed into a defense or service militia (boeitai) or were conscripted into frontline service to bolster the strength of the Japanese 32nd Army. As a result, many bodies recovered wearing Japanese military uniforms were in fact civilians. Other civilians (mostly women, the elderly, and children), did not choose death, and wandered north through the battle zone with their few possessions to American lines. This represented another problem, and many civilians were killed by unsuspecting or wary Americans, and overwhelmed the military government structure put in place behind the front lines to house them. By the beginning of June 1945, over 144,000 civilians were in U.S. custody.

Many Japanese soldiers also disguised themselves as civilians to attempt to infiltrate American lines and cause casualties;

While most of the hands-up tricks were performed by soldiers rather than civilians, some of the former were now wearing the latter's clothes....That was why all civilians between the ages of roughly ten and sixty were regarded as potential booby traps and why the prime rule was "not to take your eye off the devious gooks for a second" until they could be searched....

During the night of June 11,...civilians wrapped in dirty blankets headed toward an American unit from further south. They had nearly passed the forward positions when a vigilant sergeant sensed something wrong. He and his men raked the line with machine-gun fire, then found that many of the group were Japanese soldiers with grenades and demolition charges under their blankets.

A few days later, Anthony Cortese helped throw a heavy charge into a large cave from which no one had emerged in answer to the usual "De-te koi" calls...."We had to assume Japs were in there too, and what about them? Besides, I'd already done a cave where civilians came out first, then a Japanese soldier with his hands up. Suddenly he throws himself on the ground and the man behind him, dressed as a woman, starts firing from a Nambu strapped to the first guy's back. We all stared firing the minute he hit the ground and killed over a dozen civilians together with the two Japs--but what could you do? What you couldn't do was take chances."

Like Japanese soldiers, civilians had been instilled with the belief that the Americans were brutal captors, and that they would be raped, tortured, or even killed if taken prisoner, if the Americans chose to do so at all. It is estimated that about half of the pre-invasion civilian population of the island died, either in battle (by their own initiative, or under Japanese conscription), in accidents or friendly fire, or through mass suicide out of fear.

Camping for the night of 28 March a mile from the north tip of Tokashiki, troops of the 306th heard explosions and screams of pain in the distance. In the morning they found...more than 150 dead and dying Japanese, most of them civilians. Fathers had systematically throttled each member of their families and then disemboweled themselves with knives or hand grenades. Under one blanket lay a father, two small children, a grandfather, and a grandmother, all strangled by cloth ropes....The natives, who had been told that the invading "barbarians" would kill and rape, watched with amazement as the Americans provided food and medical care; an old man who had killed his daughter wept in bitter remorse.

The soldiers on Ie [Shima], unlike those on Kerama, had the fanatical support of the civilians, including even women with babies, who took part in suicide raids and helped defend caves and tunnels.

The Okinawa Prefectural Peace Memorial has 241,468 names, 149,456 of whom were civilians (including those conscripted into Japanese service) and 77,425 of whom were Imperial Japanese soldiers. A U.S. Army intelligence report made shortly before the invasion of Okinawa estimated that there were 65,000 Japanese troops of the 32nd Army on the island; a post-battle estimate was that 110,000 Japanese had been killed, although this may include up to 40,000 civilians conscripted by the Japanese; the official U.S. Army estimate for civilian deaths (conscripts and civilians) was 142,058. Only 7,400 Japanese soldiers surrendered, mostly in the last weeks of the battle.

Source:

Appleman, Roy E., James M. Burns, Russell A. Gugeler, and John Stevens. United States Army in World War II, the War in the Pacific, Okinawa: The Last Battle. Washington, D.C.: United States Army Center of Military History, 1948.

Feifer, George. The Battle of Okinawa: The Blood and the Bomb. Guilford: Lyons Press, 2012.

Were US soldiers in the Pacific theatre given any info regarding how "fanatic" the Japanese would be or was it all word of mouth from other soldiers? I guess what I'm asking is whether the was a "fighting the Japanese 101" class that soldiers did.