The Union sailors spotted the curious little boat shortly after 9 o’clock, just as it was closing in on the starboard beam of their ship.

It came from the east, which confused the men. Either this strange craft was a long way from home or it had come out of Charleston and somehow managed to slip through the South Atlantic Blockading Squadron. The puzzled crew tried to hail the little boat four times, but it kept coming — on a collision course for the flank of the USS New Ironsides.

The boat, which looked like a whale’s flank — albeit with a smokestack — showed no signs of replying to the crew’s hails, so the sailors opened fire with their muskets.

The boat retaliated almost immediately with small arms fire, one shot hitting the officer of the deck, Ensign C.W. Howard, who would later die. The New Ironsides crew continued to fire on the boat, but it kept coming.

When the strange craft got within 20 feet of the New Ironsides, a great explosion rocked the mighty warship off its keel.

They were under attack.

On Oct. 5, 1863 — 150 years ago today — four Confederate sailors in a small torpedo boat took on one of the U.S. Navy’s mightiest warships outside Charleston Harbor. It was one of the first attacks of its kind in history, and it accomplished two things. It gave a city struggling under siege a glimmer of hope, and it gave U.S. Navy officials heartburn.

“Among the many inventions with which I am familiar, I have seen none which have acted so perfectly at first trial,” Rear Admiral John A. Dahlgren, commander of the South Atlantic Blockading Squadron, wrote after the incident.

The David had slipped out of Charleston Harbor just after dark that evening and found the New Ironsides at anchor off Morris Island. The crew waited for the tide to turn before aiming its spar torpedo at the ship’s side.

The torpedo boat was an oddity, although it was just one of several similar vessels under construction in Charleston. The name of these boats may have been taken from one of the builders, but most people ascribed it to the Biblical tale of the man who took down the giant Goliath. It was an apt description.

The David was about 50 feet long and carried a crew of four men in an open cockpit. The cigar-shaped boat ran on steam and its jet black smokestack was the only thing that stood more than two feet above the waterline. The engine even burned anthracite coal, so that it belched clear smoke.

The David’s target that night was not coincidental. The 230-foot New Ironsides had led the attacks on Fort Sumter for most of the year, and the Confederates were desperate to take out the ship they called “Ironsides” with a mix of disdain and grudging respect. The New Ironsides carried more than a dozen big guns, was powered by sail and steam, and had metal sheeting over its hull to protect it from enemy fire.

But it could not easily fend off a point-blank attack.

The explosion from the David’s contact mine — which held 70 pounds of powder — rocked the New Ironsides to port and rattled its iron skin, but did not sink it.

The blast also threw a great deal of water into the air, some of which fell into the David’s low smokestack, extinguishing the fire for the steam engine.

Suddenly, the David was adrift and defenseless.

The captain — Lt. William T. Glassell — decided they must abandon ship. If a Navy ship found them, they were doomed. He ordered his crew into the cold, inky water.

The David’s engineer, J.H. Tombs, did not swim far before he decided that he’d rather take his chances on the crippled boat. He found another crewman, J.W. Cannon, clinging to the boat’s smokestack. Cannon could not swim. The two men worked together until finally they restarted the fire and limped back to Charleston.

Gen. P.G.T. Beauregard was ecstatic. The next day he wrote in his report that Glassell had “gallantly attempted to blow up the Ironsides with the small cigar torpedo boat.”

“Explosion occurred at proper time, but either charge was too small or torpedo too near surface,” Beauregard wrote. “Damage thus far not apparent. Lieutenant Glassell and 1 man were captured; other 2 returned safely with boat. Commotion on board the Ironsides reported very great.”

Glassell and the other crewman, James Sullivan, would not divulge information about their stealth boat. And the U.S. Navy would not talk about the true extent of the damage to the New Ironsides.

“(T)he damage done by the torpedo was much more serious than first appeared,” Dahlgren wrote a month later. “I need not urge the importance of keeping the facts from publicity.”

Eventually, the New Ironsides limped off over the horizon for repairs, and Tombs and the David became quite popular in Charleston.

But the tiny torpedo boat would not attack again until the following spring, one month after its more famous cousin — the submarine H.L. Hunley — struck another blow against the blockade.

But the David had sent the U.S. Navy a loud message. The era of the torpedo boat had arrived.