(CNN) With military tensions rising in the Middle East , more than a dozen of the most senior roles at the Pentagon lack permanent appointees and President Donald Trump is likely to be forced to name, at least temporarily, a third acting defense secretary in the coming weeks.

The Department of Defense is struggling to establish an unprecedented transition plan aimed at ensuring continuity of leadership at the highest levels while there is still no confirmed secretary of defense.

It is now increasingly likely Navy Secretary Richard Spencer will be named acting defense secretary for a brief period when Mark Esper , who is currently in the acting position following the dramatic implosion of Patrick Shanahan's nomination , is formally nominated for the permanent role. There are already plans to give Spencer highly classified briefings and secure communications to carry out the job.

The turmoil has only been heightened by the fact more than a dozen of the most senior and critical jobs at the Pentagon are filled by temporary officials.

Right now, there is no secretary of the Air Force, or permanent senior official in charge of issues as crucial as personnel and readiness; international security affairs; special operations and strategy and planning.

If Esper, who was serving as Army secretary is confirmed as Secretary of Defense, then his deputy at Army, Ryan McCarthy will have to be confirmed to fill that job as well.

In addition it is possible the Pentagon will not have a Senate confirmed vice chairman of the Joint Chiefs of Staff, the second highest military adviser to the President. General Paul Selva, the current vice chairman retires at the end of July and there is growing concern inside the department that unless General John Hyten, the expected successor can be quickly confirmed, the job will be unfilled for an extended period due to the summer congressional recess.

If it is unfilled by early September it means Hyten, a highly respected four star general who has decades of nuclear weapons experience could potentially have to revert to being a two star general until he is confirmed.

Priority to get Esper's confirmation hearing scheduled

However, the top priority is to get Mark Esper's nomination to the Senate Armed Services Committee so a confirmation hearing can be scheduled quickly.

A senior defense official emphasized key decisions are still to be made about what happens as soon as Esper's nomination goes to the Hill.

The official said the administration is expected to formally submit his nomination to the Senate in the coming days in hopes of having a confirmation vote by mid-July. However, one congressional official said given the Senate July 4 recess and the legislative schedule, it more likely a vote would take place at the end of the month.

Due to federal regulations, Esper is expected to have to instantly step down as the acting secretary of defense during that confirmation process, several officials have said. Government lawyers are looking to see if there are any loopholes that could keep him in the job through a confirmation vote, the defense official said.

It is not clear what would happen if this interim situation continues past July 31. Under federal regulations there is supposed to be a permanent secretary of defense by that date.

It is not yet clear there if there is a legal loophole, the congressional official said. They added that given the scramble was prompted by Shanahan's sudden withdrawal, the Senate Armed Services Committee is not likely to be in the mood to unduly rush the Esper confirmation even though members want a confirmation hearing scheduled as quickly as reasonably possible.

The assumption right now is that Esper steps down as soon as the nomination is submitted. The traditional practice is that the nomination would sit with the committee for seven days so there is time to schedule a hearing, ensure senators are available and receive answers to written questions submitted to Esper.

Plan to have navy secretary step in

So with the assumption Esper steps down in the interim, there is now intense internal Pentagon planning to have Navy Secretary Spencer step in as the interim acting secretary.

This would mean Spencer will have to start being completely briefed on all key issues, ranging from nuclear command and control to ongoing covert operations, to the latest intelligence on Iran. The official said the department is trying to figure out exactly when the process of briefing Spencer to be a fully qualified defense chief will begin so he is ready if Esper steps down in the interim.

If this all happens it means Esper likely will vacate the secretary of defense suite of offices in the Pentagon and go back to his former office as Army secretary. Spencer likely will leave the Navy secretary's office and move into the secretary of defense suite on the third floor of the Pentagon which has 24/7 global highly secure communications, until Esper is confirmed.

The official said as soon as the transition plan is finalized and approved by the White House, the Pentagon leadership wants to make it public so the country, as well as adversaries know exactly who holds the authorities of secretary of defense.

The transition plan currently even includes obtaining new official photographs and office door signs for Spencer, though he may only have the top job for a few days the official said.

A similar transition plan is being worked out for David Norquist who is being nominated to become deputy secretary of defense.