Use Control

By April 1961, three DoD committees had been formed to study the issue of use control: the Special Warhead Arming Control (SWAC) Committee under the Defense Atomic Support Agency (DASA), the Safety Steering Group under Dr. Marvin Stern (the Stern Committee) in the Office of Deputy Secretary of Defense for Research and Engineering, and Project 106(j), the Joint Command and Control Study Group under the Joint Chiefs of Staff (JCS). By August, all of these groups had focused on the concept of a permissive link to preclude weapon arming without the use of a controlled numerical code. At about the same time the Director of Military Applications DOE had requested a Sandia study on the availability of code-controlled special warhead arming devices._4.1

As a result of these studies, in August 1961 the Secretary of Defense formally requested the Atomic Energy Commission (AEC) to develop permissive links for North Atlantic Treaty Organization (NATO) weapons. In September 1961, the Director of Military Applications requested Sandia to continue developing the Permissive Action Link (PAL), as they had come to be called, and to report a plan for retrofitting NATO weapons with these devices. This report was delivered in January 1962._4.1

PAL, is a family of devices and subsystems designed to reduce the possibility of obtaining a nuclear detonation from a nuclear warhead without the use (insertion) of a controlled numerical code, thus reducing the probability of an unauthorized nuclear detonation._4.10

In March 1962, the JCAE convened to discuss the adequacy of existing weapon custodial arrangements. They reported an urgent requirement to develop the permissive link technology. In May, the President convened a study group under Science Advisor Jerome Wiesner to report a plan for incorporating permissive links in NATO weapons. After receiving Wiesner’s report, the President issued National Security Action Memorandum (NSAM) 160 on June 6th 1962. This order directed that all U.S. weapons deployed to NATO be equipped with permissive links. In February 1972, following a visit by members of the JCAE to the Pacific theater, the Secretary of Defense decided to extend PAL control to weapons deployed on foreign soil in the Western Pacific area._4.2

NSAM 160 also directed the establishment of a research program aimed at developing more advanced PAL devices and this initiated a program of research, development, and implementation of PAL hardware that continues into modern weapon systems. In response to NSAM 160, the DOD integrated new command and control hardware with all existing NATO-based systems. The short-range theater systems were fitted with 5-digit mechanical combination locks. The Mk31 Nike Hercules and Honest John missiles, the Mk45 and Mk54 Atomic Demolition Munitions (ADMs), the Mk54 Davy Crockett projectile, and the Mk33 and Mk48 Artillery-Fired Atomic Projectiles (AFAPs) were equipped with these locks._4.2

A crash program was initiated, not long after NSAM 160 issuance, to finish development of the electromechanical, 4-digit coded switch (MC1541) and its associated control equipment. This device, known as Category A (CAT A) PAL, was retrofitted to existing long-range systems. These included the Mk49 Jupiter IRBM, the Mk7 and Mk28 gravity bombs, and the Mk28 Mace, Mk50 Pershing, and Mk52 Sergeant tactical missiles.

National Security Presidential Directive 28, issued 2003, called for upgrading, where appropriate, safety and use control capabilities for all nuclear warheads during their refurbishment._5.1

$1.9M were approved by Congress in fiscal year 1969 for the Department of Defense for use in the development for the XM50, which was to be used for fielded atomic demolition munitions. The XM50 is a Command Arming Device (CAD) which was provided to unlock the PAL device._8.1

Two-Man Rule (Two-Person Concept)

There will be at least two individuals, both qualified in nuclear weapon operations, immediately present at all times when procedures are being performed on nuclear weapons. Two qualified individuals are considered to be present when one is in a physical position from which he can positively detect incorrect or unauthorized procedures with respect to the task and/or operation being performed by the other individual. This is known as the two-man rule._3.1

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PAL-Equipped Weapons

Locks	CAT A	CAT B	CAT B’	CAT C	CAT D	CAT D’	CAT F	CAT F’
Mk31 Mk33 Mk45-3 Mk48 Mk54	Mk50	Mk28RE Mk43-2 Mk57-2 Mk61-0			Mk28-0, 1 Mk61-2, 5, 6, 7, 8 Mk70-1, 2, 3 Mk79 Mk80-0, 1 Mk81 Mk82 Mk83		Mk61-3, 4 Mk84 Mk85

Coded Control

Prescribed Action Link (PAL) and Permissive Arming and Protective System (PAPS)

• Max Newsom was part of the PAPS Component Design Section in 1963. He also worked on the Jigsaw, Tiger, Rumpler, and PAL programs

Permissive Arming Link (PAL)_7.1

Permissive Action Link (PAL)_1.1

Sandia Digital Subsystems Software, Division 2315, did cryptographic research on command and control issues, designed and analyzed PAL code management, and designed code and key management for the T1582 PAL Controller. The Command and Control Division also did work on code and key management for the Secure Recode System and the software upgrade of the T1565 Headquarters Code Processor and the Tactical Secure Recode System._6.1

Sandia Electronic Technology Department, Division 2150, worked on the multiple-code coded switches and aircraft control equipment._9.1

Early Combination Locks

One of the first 3-digit combination locks put in place to provide additional safety in the prefiring  sequence_4.3

The Mk45 Mod 3 for the Medium Atomic Demolition Munition (MADM) used an AEC lock, the MC1885 padlock that installed on the warheads J1 connector and prevented input of electrical signals to warhead circuits._4.3

The Mk31 had two different Use Control devices that depended on its Adaptation Kit (AK). For its use on the Nike Hercules (MIM-14) missile, it used an Army Lock, the M77 Atomic Weapon Locking Device that fit onto the safing plug of the AK. For use on the Honest John (MGR-1) missile, it also uses an Army lock, the M81 Atomic Weapon Locking Device that would also fit onto the safing plug of the AK. _4.3

Two views of the M77 Atomic Weapon Locking Device for use with the Mk31 on the Nike Hercules (MIM-14) missile_4.3

Two views of the M81 Atomic Weapon Locking Device for use with the Mk31 AK on the Honest John (MGR-1) missile_4.3

The Mk54 when used as the Special Atomic Demolitions Munition (SADM), also used an AEC lock, the MC1948 lock-secured cover that included an MC1827 padlock. The cover denies unauthorized access to the arming and fuzing components._4.3

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Category A Permissive Action Link System

MC1541 T1500 T1501 T1502 T436

4-Digit Electro-Mechanical Coded Switch Decoder Recoder Controller Tester Battery

The Use Control crash-program, instigated by NSAM-160, resulted in the introduction of the first electromechanical coded switch as Category A (CAT A) PAL. CAT A PAL was a 4-digit coded switch carrying the AEC nomenclature MC1541 and its associated control equipment. The MC1541 weighs ~1.2lbs, occupies a volume of ~10 cu in., and takes between 30 seconds and 2.5 minutes to operate. A motor-driven family of gears, cams, and cam followers operate together to provide 10⁴ discrete, relative gear and cam positions. If a controller operates the motor so a proper position of the gears (code wheels) is established, the unit allows the output switches to be closed (unlock). Operating the motor to any other position off the code wheels opens the output switches (lock); the MC1541 cannot be secured in the unlock mode. Two MC1541 switches were used in each weapon for reliability. Although stockpile data has indicated that a single switch would be sufficed. Because of the lock system and variations in motor speed, each MC1541 must be controlled separately. Each MC1541 requires 7 control and monitor lines to the controller (14 per weapon). Due to the large number of circuits required for MC1541 operation, control from an aircraft cockpit was not practical._4.6

To change the MC1541 code information, it must first be unlocked and then a code change solenoid in the unit activated. When activated, this solenoid allows the code wheels to be driven to a new position corresponding to the new code. With the new code inserted, the solenoid is released; this sets the new code in the unit. Following a recode, an incorrect code must be entered to relock the MC1541._4.6

Support equipment needed to operate the both MC1541s included two controllers, the T1500 Decoder and T1501 Recoder, a controller tester, the T1502 and a power source, the T436 Battery Power Supply. All of these pieces of equipment, paired with the MC1541 associated to a weapon, constituted Category A PAL._4.4

The T1500 Controller is used to unlock and lock the MC1541 coded switches. It drives the MC1541 motor to a position consistent with the code selected and set in the T1500, it provides energy to open or close the output switches, and monitors the status of the MC1541. The T1500 weighs ~40lbs with the T436 Power Supply attached. It controls two MC1541s simultaneously from the two independent channels and indicates when at least one of the MC1541 output switch sets closes._4.5

The T1501 is similar to the T1500 decoder but has a code change capability. It selectively operates only one MC1541 coded switch at a time, first setting in the correct old code, then unlocking and preparing the switch for insertion of a new code. The new code is then set into the T1501 and the operation repeated, inserting the desired new code. An incorrect code must then be entered to relock the coded switch. This does not occur in an automated sequence but is done as separate operations for each of two coded switches in the weapons._4.5

The T1502 functionally tests the T1500A and T1501A. It simulates an MC1541 so that either the T1500A or T1501A may be evaluated for proper operation._4.8

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Category B Permissive Action Link System

MC1707 T1508 T1509 T1520 T1521 DCU-117/A DCU-121/A DCU-116/A T436

4-Digit Electro-Mechanical Coded Switch Decoder Recoder Decoder Tester Recoder Tester AMAC & PAL Aircraft Controller AMAC & PAL Aircraft Controller PAL Aircraft Controller Battery

 Category B (CAT B) PAL, 4-digit coded switch (MC1707) and its associated control equipment. This had a few distinct advantages to CAT A PAL, it could be controlled by fewer wires making it practical to be able to unlock PAL from an aircraft cockpit. It also incorporated the ability to recode and check the operational code without unlocking the PAL, decreased operation time, and a code-controlled lock operation._4.2 The MC1707, which also provided a 10₄ code population, was installed in some Mk28-RE, Mk43-2, Mk57-2, and Mk61-0 bombs._4.7 Weapons with the MC1707 can be unlocked in parallel, thus providing multiple carriage capability._4.6

As originally fielded, the CAT B PAL system included two electro-mechanical coded switches (MC1707s) in each weapon, two ground controllers (T1508 Decoder and T1509 Recoder), two controller testers (T1520 and T1521 for Decoder and Recoder, respectively), three aircraft controllers (DCU-117/A and DCU-121/A, combined AMAC and PAL, and the DCU-116/A PAL only), and a power source (T436 Battery). CAT B was installed only in bombs which have Air Force and Navy applications, although primarily Air Force. The MC1707 occupies a rectangular volume of ~18 cubic inches, weighing 2.2lbs and takes 30 seconds to operate._4.7

The T1508 Controller is designed to enable, code-check, or disenable a weapon. It can be used to check the enable/disenable condition of the weapon. The T1508 is not capable of recoding. It provides visual indications of the specific codes being utilized and of proper operations of the MC1707. Power is supplied by the T436 Power Supply which is installed in the bottom compartment prior to use._4.8

The T1509 is a controller which code-checks and recodes the coded switches of a weapon, it is not capable of an enabling operation. The T1509 provides visual indications of the specific codes being utilized and of the proper operation of the coded switches. Power is supplied by the T436 Power Supply which is installed in the bottom compartment of the unit prior to use._4.9

The T1520 and T1521 allow field certification of the operability of the T1508 Decoder and T1509 Recoder, respectively, by electronic simulation of the MC1707. The T1520 is also used to certify aircraft decoders. If the output of the T1508 is proper for that code, the T1520 will indicate the same at the end of the operation. The T1509 and T1521 operate in a similar manner except that both an old and new code are set in the units. Power for both is supplied by the T436 Power Supply which is installed in the bottom compartment prior to use._4.9

Several improvements were made in the MC1707 design to overcome problems with the CAT A PAL system. The CAT B system requires 5 wires to recode, control, and monitor a weapon instead of the 14 required by CAT A. In addition, to minimize the impact on aircraft wiring, only three wires are required to control any number of switches operating in parallel, plus one wire per weapon to monitor the weapons lock/unlock status._4.7

The CAT B system provides recode and code check capability for the stored codes without transferring the output contacts from the locked to the unlocked condition, or vice versa. Also, CAT B requires use of the stored code for a lock operation. This avoids possible accidental relock upon insertion of a wrong code after unlock. The recoders provide automated sequences of old code insertion, new code insertion, and code check operations._4.7

The subsequent fielding of Category D and F PAL resulted in requirements for back-compatibility of CAT B with newer control equipment developed for CAT D and F. CAT B PAL could be operated by the T1535 Ground Decoder, the T1535, T1555, and T1563 Recoders, the T1539 Verifier, as well as the DCU-192, 196, 201, 218, 238, and 239._4.7

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References

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