The first thing the research ship picked up in the darkness below was the trail of wreckage.

A jagged piece here, a hunk of twisted metal there. Clues, perhaps, to the demise of the mighty Japanese ships the R/V Petrel was searching for. Could this be debris from the enemy aircraft carriers as they were battered by American dive bombers?

Later, out of the gloom, a form emerged. The Petrel’s underwater robot circled it carefully, as experts studied the video feed and realized this was the Imperial Japanese Navy’s aircraft carrier Kaga, sunk at the World War II Battle of Midway.

The discovery last month of the long-lost Kaga and another Japanese carrier, the Akagi, came three weeks before the release of the new $100 million movie “Midway,” which opens Friday.

The find served as a reminder of the violence of the famous World War II sea battle, and made for a contrast between the drama on the big screen and the reality on the ocean floor.

The movie re-creates the epic June 1942 struggle in the Pacific Ocean with fitting bombast. There are explosions, grimacing pilots and bold, if mythical, pronouncements.

The sunken carriers, on the other hand, rest in the depths — shattered wrecks dripping with 70 years of sea encrustations.

The bow of the Kaga is deeply buried in the sea floor, which it struck after sinking through 17,000 feet of water. Part of its stern is gone — blown off in battle or in sinking.

Three thousand Japanese sailors and airmen died in the battle, and Japan lost its four best aircraft carriers — Kaga, Akagi, Soryu and Hiryu, according to historians Jonathan Parshall and Anthony Tully.

All four ships had been involved in the attack on Pearl Harbor six months before, which plunged the United States into World War II.