America’s first strikes on Iran were designed to be swift, stealthy and overwhelming.

B-2 bombers, F-22 fighter jets and ship-launched Tomahawk missiles delivered punishing blows to the Islamic Republic, with more than £4bn in munitions fired in the first 48 hours.

Now, the skies above Iran look very different.

Heavy B-1 and B-52 bombers have been employed, along with the U-2 Dragon Lady spy plane and EC-130H Compass Call signal jammer.

A Telegraph analysis of weapons lists published by US central command shows the shift in tactics to sustain Donald Trump’s strike campaign – and proof that they dominate the skies.

The price tag for munitions burned through during the first 48 hours of war was $5.6bn (£4.5bn), an anonymous congressional source, cited in the report by The Hill, said. For the first week, that figure stood at $11.3bn (£9bn).

According to central command’s list of the platforms used on the first days, American forces used stand-off weapons, such as ship-launched Tomahawk missiles, which can cost upwards of $1m (£800,000) each.

Greg Bagwell, a retired air marshal and president of the UK Air & Space Power Association, said: “In the early days, you want to have that instant shock.

“The easiest way to do that is fire off every Tomahawk you have in your inventory because they can arrive relatively unnoticed in a relatively quick period of time.”

He added: “The other beauty of the longer range weapons is obviously you’re not putting yourself in the threat, and therefore you keep your manned aircraft away as long as you possibly can.”

This was demonstrated by the use of stealth aircraft, such as the F-35 and B-2 bombers, in the initial stages of combat, when Iranian air defence was still working to a certain degree.

But within days of the first strikes on Feb 28, reports suggested that the threat of Tehran’s surface-to-air missile batteries had diminished enough to bring in a wider array of systems.

With air superiority, American fighter jets, bombers and spy planes are able to fly with impunity over the Islamic Republic, hunting possible targets.

This has unlocked a new type of weapon: the much cheaper gravity-dropped bombs.

Both American and Israeli jets have been photographed heading towards Iran, loaded with Joint Direct Attack Munition (JDAM)-style weapons.

Pete Hegseth, the US defence secretary, proclaimed at a March 4 press conference: “We used more exquisite stand-off munitions at the start, but no longer need to.”

While exact specifications are unavailable, stand-off weapons are those fired from outside the range of the perceived threat of enemy air defences.

Stand-in weapons are the opposite: they are dropped on targets from within range of surface-to-air threats.

JDAM is a converted dumb bomb, fitted with a mini-computer and fins, which allow GPS or laser systems to steer it.

They can glide for 10-12 miles before hitting within metres of their target.

Some estimates put the entire cost of the converted dumb bombs at between $30,000 (£24,000) and $70,000 (£56,000), a tiny fraction of an air-launched missile.

“Most of the stand-off munitions that are being used cost at least $1m each. As the campaign progresses, and Iranian air defences are further degraded, there is less need for those stand-off munitions, and they can rely more on these stand-in weapons with less range,” Colby Badhwar, a defence analyst, said.

Mr Bagwell said: “The principle is you try to get to the cheaper bombs as fast as possible, because A, you don’t have many of the longer-ranged weapons and B, it takes a long time to replace them.”

The lists suggest that American forces are now much more reliant on these weapons than they were in the initial days of the conflict.

The Trump administration has dismissed concerns about dwindling munitions stockpiles, despite the war showing no signs of slowing.

But this has not stopped murmurings from the Pentagon about the prospect of running down crucial supplies that could be used to deter a future conflict with China.

The F-15 Strike Eagles introduced into the fight are able to carry payloads of up to 23,000 lb of these gravity-dropped munitions.

Such payloads allow for a new, more sustained phase of the war in America’s eyes.

It is likely that US war planners had mapped out their strikes for the first 72 hours of the conflict.

After the initial round of strikes, you enter what is known as a “war of persistence”, according to Mr Bagwell.

“You want to be keeping aeroplanes in the sky as long as possible with as many weapons as possible, and you need to team that up with intelligence assets, like drones, like space satellites, so if anything pops up, you can whack it quickly”, he added.

After its initial barrages, the US strike campaign is likely to resemble a whack-a-mole game at the moment.

Iran has gone to great lengths to disperse and hide its drone and ballistic missile launchers.

The list of hardware published by central command mentions the U-2 Dragon Lady spy plane.

Other surveillance jets are the EC-130H Compass Call, which is capable of tracking enemy electronic signals, as well as jamming them.

The US has probably coupled its spy planes with bombers, which are also able to carry large quantities of munitions for multiple hours.

Mr Bagwell said: “The beauty of the big bombers is not that you’re necessarily going to carpet bomb huge swathes of Iran… But when you can carry 50 bombs, you can then twin that with a Reaper drone, and drop one at a time for hours on end, taking out ballistic missile and drone launchers.”

However, the former RAF commander said bombers, such as the B-52 or B-1, could only be introduced to the fight when the US was confident in its safety.

He said: “You really want to make sure they’re not going to get shot down because it’s symbolically a really bad look.

“So those bigger, non-stealthy bombers will have been kept in reserve until they felt it was safe enough.”