Crews set off a chain of carefully placed explosives Monday to break down the largest remaining span of the collapsed Francis Scott Key Bridge in Baltimore, and with a boom and a splash, the mangled steel trusses came crashing down into the river below.

The explosives flashed orange and let off plumes of black smoke upon detonation. The longest trusses toppled away from the grounded Dali container ship and slid off its bow, sending a wall of water splashing back toward the ship.

It marked a major step in freeing the ship, which has been stuck amid the wreckage since it lost power and crashed into one of the bridge’s support columns shortly after leaving Baltimore on March 26. The demolished span came crashing down on the ship’s bow and remained resting on its deck for the past six weeks.

The collapse killed six construction workers and halted most maritime traffic through Baltimore’s busy port. The controlled demolition will allow the Dali to be refloated and restore traffic through the port, which will provide relief for thousands of longshoremen, truckers and small business owners who have seen their jobs impacted by the closure.

Officials said the detonation went as planned. They said the next step in the dynamic cleanup process is to assess the few remaining trusses on the Dali’s bow and make sure none of the underwater wreckage is preventing the ship from being refloated and moved.

“It’s a lot like peeling back an onion,” said Lt. Gen. Scott Spellmon of the U.S. Army Corps of Engineers.

Officials still expect to refloat the ship within the next few days.

“This was a very big milestone for our progression forward,” said Col. Estee Pinchasin, Baltimore District Commander for the Army Corps of Engineers. She said crews don’t anticipate having to use any more explosives.

The Dali’s 21-member crew remained onboard the ship during the detonation, and no injuries or problems were reported, said Capt. David O’Connell, commander of the Port of Baltimore.

The crew members haven’t been allowed to leave the grounded vessel since the disaster. Officials said they’ve been busy maintaining the ship and assisting investigators. Of the crew members, 20 are from India and one is Sri Lankan.

In a videographic released this week, authorities said engineers were using precision cuts to control how the trusses break down. They said the method allows for “surgical precision” and is one of the safest and most efficient ways to remove steel under a high level of tension.

The National Transportation Safety Board and the FBI are conducting investigations into the bridge collapse.

Danish shipping giant Maersk had chartered the Dali for a planned trip from Baltimore to Sri Lanka, but the ship didn’t get far. Its crew sent a mayday call saying they had lost power and had no control of the steering system. Minutes later, the ship rammed into the bridge.

Officials have said the safety board investigation will focus on the ship’s electrical system.

(AP)