The nomination hearing this week for President Trump's Air Force secretary nominee was a rare sight for those monitoring Trump's progress filling Pentagon positions.

Former Rep. Heather Wilson (R-N.M.) - whose hearing was delayed several times because the White House hadn't turned in required documents - is only the second of Trump's Defense Department (DOD) picks to be interviewed by the Senate Armed Services Committee.

Trump so far has only seen one Pentagon nominee - Defense Secretary James Mattis - make it through the confirmation process and has 52 additional positions to fill. Many in the defense world are bothered by the holdup.

One defense consultant told The Hill there are rumblings that the slow pace of the process is causing the Pentagon "to kind of grind."

"It seems like at some point around March 1 it became more of a problem, the slow, tedious process in filling the posts," the consultant said.

The sluggish pace is also not missed by lawmakers.

The top lawmakers on the House Armed Services oversight subcommittee this week sent a letter to Trump urging him to fill the existing vacancies at the DOD Office of the Inspector General and Office of Special Counsel.

"We strongly encourage you to expeditiously put forth new nominees and move them through the confirmation process so that these offices can fully exercise their statutory duty to be effective and independent watchdogs," Reps. Vicky Hartzler (R-Mo.) and Seth Moulton (D-Mass.), the chairwoman and ranking member of the subcommittee, said in the letter.

And Senate Armed Services Committee Chairman John McCain (R-Ariz.) said earlier in March he is troubled by the "incredibly slow" pace.

Katherine Kidder, a military personnel expert at the Center for a New American Security, told The Hill it's much harder for DOD nominees to make it through the Senate confirmation process due to stricter rules compared to elsewhere in the government.

"The Senate Armed Services Committee has a specific rule about complete divestiture of business interests," Kidder said. "Whereas for other committees in order to get to a hearing, you can set up a blind trust, for the SASC the rules are a little more stringent, and you have to completely divest your business holdings. Because Trump has been pulling from the business community, it's kind of exacerbated the effect of that rule."

But the White House is taking far longer to put forth nominees than the previous administration. A data tracker created by The Washington Post found that as of Saturday, Trump has sent just 43 nominations government-wide to the Senate, and of those, 21 have been confirmed. More than 480 other positions across the government still need nominees.

At the same point in his administration, former President Barack Obama had sent 92 nominees to the Senate and had 37 of them confirmed.

More than two months into the Trump administration, top Pentagon jobs are mostly filled with acting officials.

The biggest problem, one defense lobbyist said, is conflict between the new Pentagon head and the White House.

The tussle became public in March when Mattis pulled his pick for undersecretary for policy, Anne Patterson, after the White House implied it would not fight a likely battle for her confirmation.

"Early on a lot of names that were floated by the Trump folks were rejected by the Mattis folks. A lot of names that Mattis floated were rejected by the Trump folks," the lobbyist told The Hill. "That really slowed things down and there's a been lot of friction between the two."

A defense industry consultant agreed, and added that Mattis has proposed picks that were outright rejected by the administration - including Democrats and those from the traditional national security establishment that were anti-Trump during the campaign.

Mattis, the consultant said, has found Trump's Pentagon offerings to be "just utterly unqualified, they don't have any background" in defense policy.

"Trying to find that combination of Republican, didn't sign a 'Never Trump' document and has some real national security background is tough and also Mattis doesn't particularly like political picks coming out, as shown by the tanking of Randy Forbes," the consultant said.

Forbes, a former Republican congressman from Virginia, was said to be in line for the Navy secretary position, but Mattis reportedly rejected him.

Trump has only nominated 12 people for DOD positions since December, including a list of six names in mid-March that included Boeing's senior vice president of supply chain and operations Patrick Shanahan, picked for deputy secretary of Defense, the Pentagon's No. 2 position.

But two of those 12 picks have already pulled out. Army Secretary nominee Vincent Viola and Navy Secretary nominee Philip Bilden both withdrew from consideration in February. They both have vast financial holdings, which would have made it difficult to meet Pentagon requirements against conflicts of interest.

"When you nominate a billionaire, it's just not a simple process," the defense industry consultant said. "When that happens, everything else backs up in the system."

Kidder said many of the names floated by the administration are from the business community, whereas "a traditional president is pulling from a community of policy experts who built their lives and portfolios keeping in mind that someday they may need to sit through a Senate confirmation hearing."

She added that the business executives "haven't necessarily organized their records in such a way that it's an easy process, not that it's an easy process for anyone."

Stricter government ethics rules for DOD jobs are also stretching out the timeline, the defense lobbyist said.

"The rules have gotten much stricter over the last eight years, which makes it very hard for nominees to comply, whereas folks like Bilden and Viola had to withdraw," the lobbyist said. "I think if this was 10 years earlier, they would not have had to."

And Trump's reliance on a relatively small campaign staff has given his administration a smaller pool of familiar faces to draw from.

"I think that they had a very lean campaign operation so that when they won they had a lean transition, but also less of a talent pool to draw from had they had a larger operation, a larger team of loyalists that other campaigns are accustomed to," the defense lobbyist said

The newly stated five-year lobbying ban for government officials is proving to be an additional obstacle.

"You're really shutting off people's options for their post-government career - that's like saying [press secretary] Sean Spicer can't be a reporter after he leaves. I think it's kind of a silly restriction," the lobbyist said. "They're putting too many roadblocks in their own path."

The lobbyist was unimpressed with the recent batch of six nominees that came out in March.

"I read the list and was like 'eh.' I didn't recognize every name that was on there," they said.

But Kidder said she saw some progress in the announcement.

"It feels like a lot of names on the slate of six is actually quite impressive and kind of signals a change toward real expertise coming into the building," she said. "Patrick Shanahan from Boeing, he may run into the same kind of business issues as Viola and Bilden did, but I think given his area of expertise, he will probably have a smooth confirmation process."

There is a light at the end of the tunnel, the defense industry consultant said. There are some 186 positions within the DOD that do not require Senate confirmation. Once the top positions make it through the confirmation process, the Pentagon should start filling up more quickly. Those individuals not requiring confirmation will still be vetted internally, "but it's going to be under a lot less political scrutiny," they said.

"I personally know a bunch of people that are in the pipeline and have not been announced. The problem is the bottleneck and some of the disagreements between the White House and the Pentagon here in getting those top slots filled, but once that's done I think everyone expects it'll move relatively quickly."

Once Wilson and the rest of the service secretaries are nominated and confirmed, the consultant said, "you'll see a very fast flood" of names. "The Trump people are not going to have as much interest, they're not going to care."

Trump is a cancer that needs to go away