TACAMO stands for "Take Charge and Move Out", a phase often used in the military and particularly by the Marines. But in the context of U.S. military aircraft, the phrase refers to a special mission and a similarly unique aircraft equipped to perform the mission. Years ago I worked on it but could not talk about it.
In the mid 1970's, when I was a young engineer at the Naval Air Development Center (NADC), this was a project I was involved with on and off over a couple year period. At the time the EC-130Q was performing this mission. My recollection was that the fleet had about 12 aircraft stations in Hawaii and Diego Garcia. The mission was to maintain a communications link between nuclear missile carrying submarines (aka "Boomers") and the U.S. command authority at all times. Communicating with submerged submarines was a challenge. You may have seen a bit of how this works if you watch the movie Crimson Tide. Remember the Emergency Action Messages (EAM) in the movie? They would be coming from this aircraft. At least one of these aircraft was in the air 7x24 since they were put into service. The existence of the mission and details of the aircraft were classified.
The project I was part of was to determine an alternative aircraft to better perform the mission. The EC-130Q was a modified version of the standard military cargo aircraft known as the C-130 Hercules, which in flown by the Marines, Navy, and Air Force. To perform this mission the standard C-130 was overloaded. These aircraft were unlikely to last long flying this mission, had some difficulties performing, and took on a higher than typical risk in each flight.
My work included comparing the performance of a number of potential "off-the-shelf" replacements for the EC-130Q. I did many virtual mission flights with differing aircraft to compare potential performance. Ultimately a modified version of the Boeing 707 (military version C-135) was selected. This "new" aircraft needed to be significantly modified to perform the mission.
After I moved on from my role at the Navy, the E-6A Mercury was introduced to replace the EC-130Q. Since then, an improved upgraded version had been put into service, the E-6B Mercury. If you see one at an airshow, which I have, look for the small TACAMO letter on the fuselage near the tail.
NAVAIR describes this aircraft as follows on their public website.
Communications relay and strategic airborne command post aircraft. Provides survivable, reliable, and endurable airborne command, control, and communications between the National Command Authority (NCA) and U.S. strategic and non-strategic forces. Two squadrons, the "Ironmen" of VQ-3 and the "Shadows" of VQ-4 deploy more than 20 aircrews from Tinker Air Force Base, Okla. to meet these requirements.
Boeing derived the E-6A from its commercial 707 to replace the aging EC-130Q in the performance of the Navy's TACAMO ("Take Charge and Move Out") mission. TACAMO links the NCA with naval ballistic missile forces during times of crisis. The aircraft carries a very low frequency communication system with dual trailing wire antennas. The Navy accepted the first E-6A in August 1989.
The E-6B was conceived as a replacement for the Air Force's Airborne Command Post due to the age of the EC-135 fleet. The E-6B modified an E-6A by adding battlestaff positions and other specialized equipment. The E-6B is a dual-mission aircraft capable of fulfilling either the TACAMO mission or the airborne strategic command post mission and is equipped with an airborne launch control system (ALCS). The ALCS is capable of launching U.S. land based intercontinental ballistic missiles. The first E-6B aircraft was accepted in December 1997 and the E-6B assumed its dual operational mission in October 1998. The E-6 fleet was completely modified to the E-6B configuration in 2003.
Primary Function: Communications relay for fleet ballistic missile submarines (A and B models) and airborne command post for U.S. Strategic forces (B model)
Contractor: The Boeing Company
Date Deployed: October 1998
Unit Cost: 141.7 million
Propulsion: Four CFM-56-2A-2 High bypass turbofans
Length: 150 feet, 4 inches (45.8 meters)
Height: 42 feet 5 inches (12.9 meters)
Wingspan: 148 feet, 4 inches (45.2 meters)
Weight: Max gross, take-off. 342,000 lbs (154,400 kg)
Airspeed: 522 knots, 600 miles (960 km) per hour
Ceiling: Above 40,000 feet
Range: 6,600 nautical miles (7,590 statute miles, 12,144 km) with 6 hours loiter time
This project was a very interesting and meaningful part of my Navy Air Engineering experience. It is nice to be able to share that these many years later. Maybe someday a few other "interesting" projects.