[1] It has a streamlined casing capable of withstanding supersonic flight and is 11 ft 8 in (3.56 m) long, with a diameter of about 13 inches (33 cm).

Due to the short time-scales, it was decided to make maximum use of off-the-shelf components such as those developed for the B57 nuclear bomb.

The Russian Continuity of Government facility at Kosvinsky Kamen, finished in early 1996, was designed to resist US earth-penetrating warheads and serves a similar role as the American Cheyenne Mountain Complex.

US aircraft cleared for its use have included the B-1 Lancer, B-2 Spirit, B-52 Stratofortress, F/A-18 Hornet, A-6 Intruder, A-4 Skyhawk, F-111, F-15E Strike Eagle and F-16 Fighting Falcon and the F-35A.

As part of NATO Nuclear Weapons Sharing, German and Italian Panavia Tornado aircraft can also carry B61s.

[14] In 2012, NATO agreed to improve the capabilities of this force with the increased accuracy of the Mod 12 upgrade and the delivery of the F-35 aircraft.

[17] The F-35A was certified to carry the B61-12 in October 2023, marking the first time a fifth generation fighter has been nuclear capable, and the first new platform in the NATO inventory to achieve such status since the early 1990s.

[18] The B61 is a variable yield ("dial-a-yield" colloquially) dual use tactical and strategic bomb equipped with Full Fuzing Option (FUFO)[1] designed for external carriage by high-speed aircraft.

[19] The B61 is armed by ground-based personnel via an access panel located on the side of the bomb, which opens to reveal nine dials, two sockets, and a T-handle which manually triggers the "command disable" function.

One of the sockets is for a MC4142 "strike enable" plug which must be inserted in order to complete critical circuits in the safety/arming and firing mechanisms.

[20] The B61 "command disable" mechanism functions as follows: after entering the correct three-digit numeric code it is then possible to turn a dial to "DI" and pull back a T-shaped handle which comes away in the user's hand.

Electrical power from the thermal battery is sufficient to "fry" the internal circuitry of the bomb, destroying critical mechanisms without causing detonation.

[33] By mass, the largest deviations from the B61-7 were the Acorn assembly, MC4137 TSSG (trajectory sensing signal generator) and the JTA (described as "ballast for WR").

The MC2969 consisted of a 14-pin ceramic-insulated bank of switches that would close upon the receipt of the proper intent unique signal (IUQS) to its electromechanical decoder.

Like the MC2969, it mechanically locked if it received the wrong input signals, but unlike the MC2969 it could only be manually unlocked, which could only take place at the factory.

The Mod 12 upgrade is being pursued as a forward-deployed tactical/strategic nuclear weapon to protect NATO and Asian allies since it can be used from dual-capable fighter aircraft, as well as planned to arm the F-35 and B-21 Raider, and its lower yield options make it more flexible with less collateral effects.

[50] In January 2014, former Air Force Chief of Staff Norton A. Schwartz stated that the Mod 12 nuclear bomb upgrade would have enhanced accuracy and a lower yield with less fallout compared to previous versions of the weapon.

An example is the higher-yield Mod 11's role of attacking underground bunkers that need a ground burst to create a crater and destroy it through the shockwave.

A 50-kiloton yield detonating on the ground produces a crater with a radius of 30–68 meters, depending on the density of the surface, effectively putting the bunker within the circular error probability.

[51] In 2014 critics said that a more accurate and less destructive nuclear weapon would make leaders less cautious about deploying it, while Schwartz said it would deter adversaries more because the U.S. would be more willing to use it in situations where necessary.

F-16 and Panavia Tornado aircraft cannot interface with the new bomb due to electronic differences, but NATO countries buying the F-35 would be able to utilize it.

[56] In October 2018, the Mod 12 guided tail-kit assembly received Milestone C approval to enter the production phase; the TKA went through the traditional test program in under 11 months, achieving a 100% success rate for all 31 bomb drops.

[59] This drew criticism from the Russian Deputy Minister of Foreign Affairs Alexander Grushko, who accused the US government of "reducing the nuclear threshold" with the weapon's increased accuracy.

[60] Initially, the NNSA Stockpile Stewardship and Management Plan anticipated Phase 1 development for the B61 Mod 13 Life Extension Program (LEP) beginning in 2037 with first production of the weapon in 2050,[22] but in 2023 plans were announced to produce a new gravity bomb similar to that of the B61-12, but having a high yield similar to that of the B61-7, named the B61 Mod 13.

[62] A W61 Earth Penetrator Warhead (EPW) with a yield of 340 kilotonnes of TNT (1,400 TJ) was developed for the AGM-129 Advanced Cruise Missile and the MGM-134 Midgetman small ICBM.

[66] In May 2010 the National Nuclear Security Administration asked Congress for $40 million to redesign the bomb to enable the Lockheed Martin F-35 Lightning II to carry the weapon internally by 2017.

[71] Boeing will use their experience with the Joint Direct Attack Munition to yield JDAM-equivalent accuracy in a nuclear bomb.

[72] This contract is only the first part of the billion-dollar expense of producing and applying the tail kits, over and above the $10 billion cost to refurbish the warheads.

On 1 July 2015, the National Nuclear Security Administration (NNSA) conducted the first of three flight tests of the Mod 12 tail kit assembly.