1 in 3 chance that US will strike Iran by end of April
Sentinel forecasters jointly estimate that there is a 36% chance (range, 25%-60%) that the US will launch airstrikes against nuclear weapons program facilities in Iran by the end of April, starting most likely between April 10 and April 25 and ending likely before May 1.
The US military is bringing approximately six B-2 stealth bombers to a joint US-UK military base on Diego Garcia, an island in the Indian Ocean that is well-positioned for staging attacks on either Yemen or Iran. The B-2 bomber is one of the only US military aircraft capable of carrying the GBU-57A/B MOP, the largest of the US "bunker buster" bombs that can penetrate fortified underground facilities; it can also drop a wide range of other bombs, including smaller bunker busters. In addition, three C-17 cargo aircraft have flown to Diego Garcia to support the B-2s, and one to support KC-135 Stratotankers that refuel B-2s; three additional C-17s have flown to Diego Garcia for unknown purposes. Seven KC-135s and one other aircraft are parked on Diego Garcia as of this writing.
The current buildup of B-2 bombers in Diego Garcia is large and very unusual. It is possible that the bombers are staging for missions against the Houthis in Yemen, though this might not be the case for two reasons: First, the US conducted strikes against fortified underground targets in Yemen in October 2024 and January 2025, and while more underground targets likely remain, a large mission to target underground Houthi locations seems like overkill. Second, for the October 2024 airstrikes in Yemen, B-2s were likely deployed directly from Missouri, not Diego Garcia, and B-2s were not used in the January 2025 airstrikes; current preparations are much larger-scale and different.
As a result, our forecasters think that it’s a live possibility that Iran is the target of a planned operation involving B-2 bombers. Conditional on an attack in Iran, fortified underground locations of importance to Iran's nuclear weapons program are the most likely targets, although Iran's newly revealed underground missile base could also be targeted. If an operation does go forward, we would expect to see the use of bunker-busting bombs dropped by the B-2s, together with smaller bombs, missiles, and drones, in a coordinated effort across military services.
A number of different military assets are also undoubtedly being readied for use in any upcoming operation involving the B-2s. The USS Carl Vinson carrier strike group arrived in Guam on March 24 and has been ordered to the Middle East, perhaps to participate in any operation involving the B-2s and to provide protection for Saudi oil installations and for Israel from Iranian and Houthi missile and drone attacks in the aftermath of a potential attack on Iran.
Carrier strike groups have previously stayed in port in Guam for four days, and the transit time from Guam to the Middle East is about two to three weeks; one official estimated that the USS Vinson would arrive in the Middle East in "early April." If B-2 missions will wait for the USS Vinson to arrive in the Middle East, which is likely, then the earliest possible start date for the operation would be approximately April 10.
One of four US guided-missile subs was also spotted coming up for air in Hawaii and could be headed to the region. At least one sub will likely be in the region before any operation starts, and any subs will likely arrive on their own schedules as well.
On the other hand, we are also mindful of the low baserate for a US administration directly attacking Iran. We also considered modelling the administration as being dispositionally very over the top. The cost in terms of money, time between home port maintenance and replenishment, and extended deployment for an extra carrier strike group is not small1, and B-2 operation and maintenance is also not cheap2. But this cost has its own purity of logic for forcing Iran to come to the negotiating table for real or watch bombs drop—without ultimately requiring the bombs if Iran blinks first.
In a letter delivered to Iran's Supreme Leader Ali Khamenei on March 12, the Trump administration gave the country a two-month deadline to reach a new nuclear agreement. Discussing the letter, Trump said, "We can't let them have a nuclear weapon. Something is going to happen very soon. I would rather have a peace deal than the other option, but the other option will solve the problem." As of this writing, Iran is considering negotiations, but the country does not want to appear to be capitulating to US demands.
A flight notice (NOTAM) has been issued for Diego Garcia that restricts the use of two aircraft parking spaces through May 1, suggesting that any operation that occurs is planned to be wrapped up before that date. A planned operation of this size will take more than one day, so it will likely start well before April 30 if it happens. Of course, NOTAMs and orders can be changed at any time, but it's currently likely that any operation will start no later than April 25.
Consistent with this timeframe, Newsweek also reported that the USS Harry S. Truman's deployment in the Middle East has been extended for another month; the carrier strike group had been scheduled to return to Virginia at the end of March. The US wants that carrier to stay in the region through "at least" the end of April.
Thus, the most likely date range for the start of the planned operation is April 10-25, if the operation goes forward.
It should be noted that we see no evidence of troop buildups. The planned operation is not an invasion. Its purpose is clearly to strike a specific list of targets. However, we do not rule out regime change as a possible additional goal; it is possible, if very unlikely, that the US could be partnering with groups inside Iran to form a new government.
We at Sentinel are particularly focused on the largest-scale risks. We’ll be considering those in more depth by the time we publish our weekly briefing on Monday. Briefly, the US has the capacity to decisively win on one or two fronts at a time, so its strategic logic leads it to want to wrap up conflicts in order: put an end to the Ukraine war, and address Iran next, to preserve its ability to respond to a Chinese invasion of Taiwan. The logic of its rivals is then the opposite: to tightly coordinate and threaten to expand conflicts on each front so that the US can’t effectively respond to any. This is a path to a world war.
Pilot writes to clarify that NOTAM not that reliable:
> Hello, civilian pilot here. You say that a NOTAM expiration of May 1 means it is "likely" that any operation will be completed by then, but that is putting too much weight on this information. NOTAMs are used for short-range flight planning, hours or days in the future. Expiration dates more than a few days out are often just a placeholder, since you have to file some expiration date. It's not unusual at all for NOTAMs with expiration dates months in the future to be abruptly cancelled, or for NOTAMs with expirations a week in the future to be reissued for much longer terms.
> As a concrete example, Beale AFB has a TFR to keep visual flights out of the way of its drone operations (formerly Global Hawks, now vague). Currently this expires November 2, but it's been reissued for years continuously with updated expiration dates. I would not infer anything about drones leaving Beale by November, or staying at Beale through November. Even if they were planning to transfer them out, we would probably not learn this until it had already happened and the TFR was cancelled.
> There just isn't much effort put into maintaining this as a future calendar of events, since that is not how this system is used. Even mundane construction and maintenance projects at civil airports have largely inaccurate expiration dates in the NOTAM system.
> Thanks for your newsletter; it's insightful.
Iran reaching back to the US: https://www.reuters.com/world/middle-east/irans-foreign-minister-says-tehran-sent-response-trumps-letter-through-oman-irna-2025-03-27/