The Marine Corps said it grounded its CH-53E Super Stallion helicopters from training in Hawaii for 19 days and pulled them from an Australia deployment after the Jan. 14 crash of two of the big choppers off the North Shore of Oahu killed all 12 aboard.

The Corps maintains, however, that the helicopters remain safe to fly.

The return to flight in Hawaii came amid the ongoing mystery of why the two choppers apparently collided in a fireball 2 miles off the coast and revelations that Marine Corps aviation — including fixed-wing F/A-18 Hornets as well as rotary aircraft — has been hamstrung by budget cuts leading to parts shortages and maintenance backlogs.

“In general, across the Marine Corps aviation enterprise, we have challenges” — with the CH-53 helicopter community being “the most challenged,” Marine Corps Commandant Gen. Robert Neller told a Senate subcommittee last month.

Sen. Dick Durbin, a Democrat from Illinois, said that between May 2014 and September 2015, 18 Marines were killed in 13 separate aviation incidents.

An investigation into the cause of the Jan. 14 crashes of the Marine Heavy Helicopter Squadron 463 choppers is ongoing, the Marines said. Meanwhile, funerals are being held across the country after mostly minimal remains of the Marines were found and the Corps ended its search at sea April 4.

Lisa and Mike De La Cruz, the parents of one of the lost Marines, Sgt. Dillon Semolina, a 24-year-old crew chief, said the two choppers shouldn’t have been flying that night because the parts issue was so bad.

“In the wake of the 14 January mishap, the squadron commanding officer canceled all flights to allow the squadron personnel to focus their attention on the active search and rescue effort, the squadron memorial, and the obligation they had to support the families of the lost Marines,” said Capt. Cassandra Gesecki, a spokeswoman for the III Marine Expeditionary Force in Okinawa, Japan.

HMH-463, which had 12 helicopters before the crash, “stopped all flight operations for 12 days and then only conducted functional check-flights required in support of maintenance-related operations,” Gesecki said in an email. “There were no training or operational support flights flown for a total of 19 days.”

An inquiry made on behalf of the De La Cruzes by Minnesota U.S. Sen. Al Franken’s office reported that the HMH-463 commander pulled the squadron out of deployment rotation and began “a complete work-up from the ground up on HMH-463’s flight operations to ensure qualification and proficiency.”

“The improved material readiness of the aircraft in HMH-463 is a function of its deliberate efforts in the wake of the mishap and a reduced operational tasking,” Gesecki said. The reduced tasking was ordered by the commanding general of the 1st Marine Aircraft Wing in coordination with the commanding generals of III Marine Expeditionary Force and Marine Corps Forces Pacific, she said.

“By reducing their requirements to support other local units, they have been able to focus internally on readiness, training pilots, aircrew and maintainers,” Gesecki said.

Franken’s office said that the landing gear failed to rotate down on one of the CH-53s in December. Eventually, the crew was able to lower the gear. Mike De La Cruz, who lives in Minnesota, provided pictures from a CH-53 in Hawaii that he said had to make an emergency landing March 5 when a several-foot flap ripped open on its fuselage.

The Marine Corps said a CH-53 made a “precaution-ary” landing “due to a fiberglass engine cowling latch that failed.”

“The aircrew handled this incident in accordance with prescribed operating manual guidelines and landed nearby,” Gesecki said. The squadron also had an aircraft make a precautionary landing due to a caution light, she said.

HMH-463 made one emergency landing and the two precautionary landings in the last six months, Gesecki said. The emergency landing was not explained.

De La Cruz, a former Marine Corps CH-53 crew chief in Operation Desert Storm, said in talking with Marines, a picture emerged of a barely functioning unit.

They didn’t “have any parts to replace anything, to repair anything of any sort,” De La Cruz said. “So what they were doing was robbing Peter to pay Paul” — taking parts from one chopper to keep another in the air.

“And it’s a vicious circle where they are just scrambling to find anything they can,” he said. “In front of the hangar they have basically skeleton helicopters that they’ve robbed so many parts out of that they don’t even look like helicopters anymore.”

Three days before the crash, Lt. Col. Edward Pavelka, commander of HMH-463, was relieved of command. Higher command had “lost confidence in his ability to continue to lead the squadron,” the Marine Corps said without explaining what Pavelka had done.

The inquiry by Franken’s office said Pavelka was removed because the squadron had low unit morale and low readiness.

De La Cruz said he was told Pavelka was flying the helicopters minimally because of safety concerns.

“We cannot speculate on secondhand knowledge,” Gesecki said in response. No more information would be available until an aviation mishap board has completed its investigation, she said.

HMH-463 had deployed four of its big troop-carrying helicopters in 2014 and 2015 to Darwin, Australia, for ongoing rotations and a Marine Corps presence in the country. Marines with the 1st Battalion, 1st Marine Regiment out of Camp Pendleton, Calif., arrived in Darwin on April 13 to begin the latest deployment of about 1,250 Marines there.

HMH-463 was scheduled to fulfill a portion of the aviation role for that fifth iteration of the mission along with a detachment from Marine Light Attack Helicopter Squadron 367, also based at Kaneohe Bay, Gesecki said.

“After the January mishap, the decision was made to replace HMH-463 in this rotation with additional aircraft from HMLA-367,” she said. Four much smaller UH-1Y Venom helicopters and about 120 Hawaii personnel were expected to head to Darwin last week.

The deployment of Venom helicopters will allow Australian army hosts to experience wider aircraft roles such as firing weapons for close air support, the Marines said.

Neller, the Marine Corps commandant, said at the March hearing that “we have a plan, and we believe we have sufficient funding” to tackle the maintenance backlog. “It’s just not going to happen overnight.”

Asked about HMH-463’s remaining aircraft, Gesecki said, “Yes, they are safe to fly.” The aircraft used for training “are flown only after a thorough set of inspections. There will always be inherent risk in military aviation. The Marine Corps remains committed to ensuring the safety of our aircrews and the air worthiness of all our aircraft.”