Before being damaged, it carried Interstate 695, a beltway around Baltimore;[9] its four lanes (two in each direction[10]) were used by some 34,000 vehicles each day, including 3,000 trucks, many of which hauled hazardous materials barred from the two harbor tunnels.

[11][12] The bridge crossed one of the busiest shipping routes in the United States: the lower Patapsco River, which connects the Port of Baltimore to the Chesapeake Bay and the Atlantic Ocean.

[21] Once in service, Dali had undergone 27 inspections at ports globally,[22][23] including two in 2023: one in June in San Antonio, Chile, where a fuel-pressure gauge was repaired, and the second in September by the U.S. Coast Guard in New York, which found no problems.

[55] At 1:27 a.m., a mayday call was made from the ship,[54] notifying the Maryland Department of Transportation that the crew had lost propulsion and control of the vessel and that a collision with the bridge was possible.

[62] The Maritime and Port Authority of Singapore (MPA) reported that the ship dropped anchor before hitting the bridge, as part of its emergency procedures.

[66] Emergency teams began receiving 911 calls at 1:30 a.m.[57] The Baltimore Police Department was alerted to the collapse at 1:35 a.m. Large rescue and recovery efforts were begun.

[78] The bridge's continuous truss relied on its overall structure to maintain integrity; in engineering terms, it was fracture critical, meaning it had no redundancy against removal of support of any particular part of it.

[101] On May 1, a fifth body, belonging to Miguel Angel Luna Gonzalez, 49, of Glen Burnie, was recovered from a red truck that had been among the missing construction vehicles.

[83] Groups such as the Baltimore International Seafarers' Center made efforts to support the crew members as they remained on the boat,[106] including providing them with Wi-Fi hotspots.

[112] NTSB personnel boarded the ship late on March 26 and obtained the voyage data recorder (VDR), which would help investigators develop a timeline of events leading up to the collision.

[115][116][117] At a Senate Commerce Committee hearing on April 10, NTSB Chair Jennifer Homendy said the agency would not likely issue its preliminary report until the first week of May.

She said investigators were gathering data about the ship's electrical system, examining its circuit breakers with the assistance of Dali shipbuilder Hyundai Heavy Industries, and comparing the bridge's design and pier protection to current regulatory standards.

[118][119] On April 15, FBI agents searched Dali in a criminal investigation to establish whether the crew left the port aware that the ship had problems with its electrical or mechanical systems.

[132] On September 21, FBI agents in Baltimore boarded Maersk Saltro, a ship owned by Synergy Marine Group, the owner of Dali.

[134] Only one part of the Port of Baltimore was unaffected: the Tradepoint Atlantic marine terminal at Sparrows Point, on the seaward side of the Key Bridge.

[48][154][155] Vehicles that are carrying hazardous loads or are too tall for the tunnels are detoured along the western section of I-695,[156] bypassing from the north and west the entire city of Baltimore.

[165] On April 12, Moore issued an executive order under the law to start a $12.5 million program operated by the Maryland Department of Labor to prevent layoffs by port businesses.

[173][176] On April 17, Grace Ocean Private filed a general average declaration to require cargo owners to cover part of the salvage costs.

[178] On April 22, city officials filed papers accusing Grace Ocean Private and Synergy Marine of negligence,[179] claiming the ship was unseaworthy and had an incompetent crew who ignored warnings of an inconsistent power supply before leaving port.

[181] On April 25, a Baltimore-based publishing company sued Grace Ocean and Synergy Marine in a class-action lawsuit that seeks damages for local businesses whose revenues were reduced by the collapse.

[184][6] On September 18, Brawner Builders, the construction company that employed workers who died in the collapse, sued Grace Ocean and Synergy Marine for negligence and sought damages.

[189][190] On October 24, the department announced that Grace Ocean and Synergy Marine had agreed to pay $101.9 million to settle the government's civil claims.

[193] That same day, the Maryland state government sued the companies, seeking punitive damages and compensation for: the total replacement cost for the bridge; expenses for the emergency response, salvage, bridge demolition, unemployment insurance, and business interruption relief; lost revenue from tolls, fees, and taxes; other economic losses; and environmental and infrastructure damage.

[66] U.S. Secretary of Transportation Pete Buttigieg contacted Maryland governor Wes Moore and Baltimore mayor Brandon Scott to offer his department's support.

[8] On March 27, Moore and Biden thanked Dali's crew for transmitting the mayday call warning of the ship's power failure and the impending collision.

[91] Biden visited the site on April 5; he surveyed the wreckage from Marine One and was later briefed by officials from the local government, the Coast Guard and USACE.

[218] The next day, the first work vessel used the alternate channel: a tugboat pushing a fuel barge to Dover Air Force Base in Delaware.

The salvage and recovery flotilla had grown to 36 barges, 27 tugboats, 22 floating cranes, 10 excavators, one dredger, one skimmer, and three Coast Guard cutters.

[43] The preliminary NTSB report stated that the agency was working with the Maryland Transportation Authority to study short-term and long-term modifications to the pier protection system for the Chesapeake Bay Bridge.

[51][52] By April 11, the Maryland Port Administration had begun consulting tugboat operators about potential modifications to protocol, which would depend upon recommendations from the NTSB and the Coast Guard.