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US Demonstrates Nuclear Second-Strike Capability in Giant Pace 25-1 Exercise.
On April 11, 2025, the U.S. Air Force announced the completion of exercise Giant Pace 25-1, a critical test of the airborne nuclear command and control system conducted by the 625th Strategic Operations Squadron (STOS), based at Offutt Air Force Base, Nebraska. Assigned to the 95th Wing, this squadron plays a key role in the U.S. nuclear deterrence posture by ensuring the President can reliably issue launch orders for the nation's intercontinental ballistic missiles (ICBMs), even under degraded or extreme conditions.
The Giant Pace exercise's main objective is to validate the effectiveness of the Airborne Launch Control System (ALCS), a capability hosted aboard the U.S. Navy’s E-6B Mercury aircraft. (Picture source: US DoD)
The Giant Pace exercise, officially referred to as Simulated Electronic Launch Minuteman (SELM), is conducted twice a year. It is not a response to any specific geopolitical event but rather the result of a long-term planning cycle, sometimes extending up to five years. Its main objective is to validate the effectiveness of the Airborne Launch Control System (ALCS), a capability hosted aboard the U.S. Navy’s E-6B Mercury aircraft. This system is designed to maintain continuity of nuclear command if ground-based command centers are destroyed or rendered inoperative. During this iteration, the 625th STOS coordinated the airborne operations of the test, which took place on April 9, 2025, at Offutt Air Force Base.
The squadron’s mission goes beyond planning: it develops and validates the targeting instructions for ICBMs, ensuring their precision and operational readiness. It also provides qualified personnel and dedicated systems for ALCS missions. SELM preparation involves multiple stakeholders, including the 576th Flight Test Squadron and the 377th Test and Evaluation Group, both located at Vandenberg Space Force Base in California, alongside support from the 90th Missile Wing at F.E. Warren AFB, Wyoming. Oversight and support are provided by Air Force Global Strike Command and the Air Force Nuclear Weapons Center.
Although no live warhead is launched, every operational step up to the simulated launch is executed under authentic conditions. For many operators, this is a rare opportunity to apply their technical training in a high-fidelity environment. The test begins at one of six missile launch facilities and involves two launch control centers to assess the integrity of cabling, communication systems, and the mechanical elements that transmit launch orders.
To maintain readiness, operators undergo continuous training and certification. This includes regular communication checks with missile crews, validation of system updates, and an annual live missile test from Vandenberg. These procedures are managed by the squadron’s training and evaluation team, which ensures operators are fully prepared to carry out their mission if required.
The U.S. second-strike capability relies on a nuclear triad of land-based Minuteman III missiles, stealthy Ohio-class submarines with Trident II missiles, and strategic bombers, all designed to ensure a survivable and effective retaliatory response (Picture source: US DoD)
The airborne segment of the test is overseen by a mission director aboard the aircraft, in this case Captain Ryan Saunders, test and analysis engineer with the 625th STOS. He is responsible for overall test management in the air, including command authentication, radio verification, crew coordination, communication with ground stations, test sequence progression, and initiation of simulated launch commands. The ALCS team includes other specialists such as flight path controllers, data collectors, and ground communication operators.
Due to the complexity of SELM, flawless coordination and situational awareness are critical. Each test iteration brings new variables and aims to validate emerging procedures and technical capabilities. ALCS operator Captain Cory Sylvester highlighted the rare nature of the exercise, noting that it provides a concrete view of years of training and operational preparation, from both airborne and ground perspectives.
The ALCS mission depends on close cooperation with the U.S. Navy, particularly the Fleet Air Reconnaissance Squadrons VQ-3 and VQ-4, which operate the E-6B aircraft. This inter-service coordination ensures aircraft availability, integration of appropriate equipment, and execution of test protocols according to plan.
Giant Pace remains an essential element in sustaining the credibility of U.S. nuclear deterrence. By proving that launch orders can be transmitted to ICBM units from airborne platforms even if ground-based command nodes are destroyed, the exercise reinforces the concept of assured second-strike capability. This capability is central to deterring any adversary from considering a first-strike option.
The U.S. second-strike capability is grounded in its nuclear triad, consisting of land-based ICBMs, strategic submarines, and long-range bombers. The land component, which plays a particularly critical role in exercises like SELM, includes approximately 400 Minuteman III missiles deployed in hardened silos across Montana, North Dakota, and Wyoming. These missiles are on constant alert and can be launched within minutes, serving as an immediate and highly responsive deterrent.
Alongside the land-based force, the sea-based component includes Ohio-class submarines equipped with Trident II D5 missiles, operating undetected across global waters. These vessels ensure survivability through mobility and stealth. The air component includes B-52H and B-2 bombers armed with nuclear gravity bombs and cruise missiles, providing flexible response options. All three components are designed to survive an initial attack and respond with overwhelming force.
The U.S. operates hardened ground-based command centers, but also maintains airborne command platforms such as the E-4B “Nightwatch” and E-6B Mercury (Picture source: US DoD)
Beyond delivery systems, the ability to communicate and command under crisis is fundamental to second-strike assurance. The U.S. operates hardened ground-based command centers, but also maintains airborne command platforms such as the E-4B “Nightwatch” and E-6B Mercury. These aircraft, along with redundant communication networks—ranging from satellite links to very low frequency (VLF) systems—ensure the President and military leadership can issue orders even in the most degraded conditions.
In summary, the U.S. second-strike capability is built on a resilient combination of technical infrastructure, strategic doctrine, and operational readiness. Exercise Giant Pace 25-1 reflects this approach, testing every link in the decision-making chain and the survivability of command systems. Through rigorous execution, inter-service cooperation, and the validation of key systems such as ALCS, the 625th STOS ensures the U.S. nuclear posture remains credible, adaptable, and effective.
As strategic tensions escalate in regions such as Ukraine, the Indo-Pacific, and the Middle East, demonstrating the ability to respond to a nuclear attack under any scenario has gained renewed significance. Giant Pace 25-1 underscores the United States' resolve to maintain a functional and survivable nuclear command and control structure. Faced with evolving threats—including conventional decapitation strikes and cyberattacks targeting command systems—this type of exercise affirms that the U.S. deterrent is not only intact but also actively validated. In an increasingly unstable security environment, such demonstrations contribute both to national defense and to global strategic stability by signaling that any aggression would trigger a capable and coordinated response.