References Consulted:
Designation-Systems.Net Article on UGM-27 Polaris by Andreas Parsch
Designation-Systems.Net Article on UGM-73 Poiseidon by Andreas Parsch
Designation-Systems.Net Article on UGM-96 Trident I by Andreas Parsch
Designation-Systems.Net Article on UGM-133 Trident II by Andreas Parsch
From Polaris to Trident: The Development of US Fleet Ballistic Missile Technology by Graham Spinardi
U.S. Nuclear Weapons: The Secret History by Chuck Hansen
Characteristics of Tactical, Strategic, and Research Missiles, 22 April 1957 (4.47 MB)

System Reliability of Early SLBMs

The next time you hear someone talk about deploying only “proven and reliable” missile defense systems; think about this for a moment.

The first SLBMs the U.S. Navy deployed - the Polaris A-1s; had less than 50% reliability. That meant out of 16 SLBMs on a SSBN, only eight (at best) would successfully launch and complete their missions. It took nearly two years before the next version of Polaris, the A-2 entered service, with a reliability of about 63-65%. Another two years passed before the next version, the A-3; arrived, with a reliability of about 79-82%.

Unfortunately, for this entire period; the W47 warhead was carried by the Polaris missile fleet; and this was a very troubled warhead. One specific model; the W47 Y2 Mod 2, which in 1965 made up 3/4ths of the W47 stockpile; had a dud rate of 75%! This meant that the overall W47 stockpile would only work 50% of the time (assuming that the earlier W47 Y1s which made up a quarter of the stockpile still worked).

To correct this problem, the AEC began to rebuild the whole stockpile of W47s (some 300 warheads), beginning in March 1965 to the W47 Y2 Mod 3 configuration. This fix was not achieved until late 1967.

To put things in context; from 1960 to 1967, the U.S. Navy deployed an unreliable weapons system on it's SSBNs at great cost. Either the missile wouldn't work – or when it did, the warhead wouldn't work.

SLBM Deployment

The reason the U.S. Navy wanted forty-five SSBNs in the Sixties was because they would break down nicely and provide a neat structure of five squadrons containing nine submarines each.

UGM-27A Polaris A-1

Start of Service: 15 November 1960
End of Service: 14 October 1965

Missile Length: 342”
Missile Diameter: 54”
Missile Weight: 28,800 lbs

Missile Thrust (Second Stage): 31,000~ lbf for 65 seconds. Total Impulse of 2,000,000 (lbs x sec).
Missile Thrust (First Stage): 63,000~ lbf for 60 seconds. Total Impulse of 3,800,000 (lbs x sec).

Propellant (Second Stage): 7,300 lbs of polyurethane propellant mixed in with ammonium perchlorate (NH₄ClO₄) oxidizer and aluminum additives. ISP of 240.
Propellant (First Stage): 15,200 lbs of polyurethane propellant mixed in with ammonium perchlorate (NH₄ClO₄) oxidizer and aluminum additives. ISP of 240.

Stage Empty Weight (Second Stage): 2,100 lbs with a Steel motor case (this figure includes various airframe elements not just the motor casing)
Stage Empty Weight (First Stage): 3,200 lbs with a Steel motor case (this figure includes various airframe elements not just the motor casing)

Warhead: W47 (600 kt) weighing 600 lbs, with 250 lbs for re-entry shielding, etc.
Range: 1,200 nautical miles
CEP: 900 meters (3,000 feet)

UGM-27B Polaris A-2

Start of Service: 26 June 1962
End of Service: 1 November 1974

Missile Length: 372”
Missile Diameter: 54”
Missile Weight: 32,500 lbs

Propellant (Second Stage): 7,400 lbs of composite double base propellant with Nitrocellulose, Nitroglycerin, ammonium perchlorate (NH₄ClO₄) oxidizer and aluminum additives.
Propellant (First Stage): 19,200 lbs of polyurethane propellant mixed in with ammonium perchlorate (NH₄ClO₄) oxidizer and aluminum additives. ISP of 240.

Stage Empty Weight (Second Stage): 1,900 lbs with a Fiberglass/epoxy motor case (this figure includes various airframe elements not just the motor casing)
Stage Empty Weight (First Stage): 3,200 lbs with a Steel motor case (this figure includes various airframe elements not just the motor casing)

Warhead: W47 (600 kt) weighing 600 lbs, with 185 lbs for re-entry shielding, etc.
Range: 1,500 nautical miles
CEP: 900 meters (3,000 feet)

Notes: The first stage was increased by 30 inches over the A1's first stage, taking advantage of space originally set aside for buoyancy compensation tanks. The Polaris A-2 was the only U.S. Ballistic missile to actually enter operational service with Penetration Aids. One SSBN loadout went to sea briefly equipped with PX-1 Penetration Aids. They were withdrawn shortly after that initial deployment.

UGM-27C Polaris A-3

Start of Service: 28 September 1964
End of Service: October 1981

Missile Length: 388”
Missile Diameter: 54”
Missile Weight: 35,700 lbs

Propellant (Second Stage): 9,000 lbs of composite double base propellant with Nitrocellulose, Nitroglycerin, ammonium perchlorate (NH₄ClO₄) oxidizer and aluminum additives.
Propellant (First Stage): 21,800 lbs of polyurethane propellant mixed in with ammonium perchlorate (NH₄ClO₄) oxidizer and aluminum additives. ISP of 240.

Stage Empty Weight (Second Stage): 1,800 lbs with a Fiberglass/epoxy motor case (this figure includes various airframe elements not just the motor casing)
Stage Empty Weight (First Stage): 2,800 lbs with a Fiberglass/epoxy motor case (this figure includes various airframe elements not just the motor casing)

Warheads:3 x W-58 (200 kT) in 3 x MK 2 RVs.
Range: 2,500 nautical miles
CEP: 600 meters (1,968 feet)

Notes: Major changes were made in the A3's warhead section as a result of the US Navy's Special Project Office's plan for the A3 to meet the original specifications of Polaris (2,500 nm range, and 1 megaton warhead), which had been allowed to be reduced in favor of faster deployment.

Because of the unofficial Nuclear Test Ban moratorium between the US and USSR during the A-3's development cycle, it was impossible to test a new warhead design, and within the Navy, there were two primary reasons for not using the US Air Force's Mk 11 re-entry vehicle with a 2 megaton W-56 warhead, despite it's availability:

* The US deterrent (Polaris/Minuteman) would be reliant on a single re-entry vehicle design; and thus subject to a significant degradation if unforeseen problems arose with the RV.

* The Mk 11 was an Air Force design.

Finally, a solution was found to the seemingly intractable problem. Rather than using one big warhead; use multiple smaller ones. Calculations soon showed that three 200 kiloton W-58 devices initiating in a triangular pattern would produce 7 PSI (the level of overpressure considered necessary at the time to demolish buildings) over the same area covered by a one megaton initiation.

It was at this time that penetration of ABM defenses raised it's head, and the designers were forced to make a decision between a re-entry pattern optimized for maximum destruction, and one optimized so a NIKE-ZEUS style interceptor could not kill all three warheads with a single initiation.

What was settled on was a fixed mechanical system that when the missile bus reached the velocity needed to hit the target with it's warheads, the three re-entry vehicles tilted outwards and were jettisoned in a pattern which would result in a minimum distance of one mile between each warhead almost immediately after jettisoning.

While this degraded the efficiency of the triangular “claw” pattern, it was felt that it was needed to ensure that at least one warhead would make it through a NIKE-ZEUS style defense.

Unfortunately, while this was an elegant solution to the problem of a NIKE-ZEUS intercept, the engineers had made a serious error. Because they had selected NIKE-ZEUS as the target platform to defend against, all of their calculations had been made around the effects of a 20 kiloton warhead, as was employed on NIKE-ZEUS.

Thus, when the Soviets did not introduce a NIKE-ZEUS style ABM system, but the A-135 (ABM-1 GALOSH), with a 1 megaton warhead, followed by the US Army with it's Nike-EX/Spartan missile with a 5 megaton warhead; all of the careful work that had gone into the separation pattern were completely wasted.

Additionally, the fact that the decoys designed for the Polaris A-2 (PX-1) had turned out to be completely wrong for the threat they now faced, was a major decision in deciding not to implement the PX-2 penetration aid package on the A-3; despite 300 pounds of weight being allocated for it on the PBCS.

Note II: As a small side note; the US Navy actually received several sets of in-flight reliability reporting systems designated PY-3 in 1968. They were housed in the equipment section of the missile, and following a successful RV deployment, would be ejected upon which they would transmit back this information to the SSBN. It was not deployed because submariners' felt that the requirement to run up a receiving antenna would compromise SSBN concealment. (Ed note: Like the launch of all 16 tubes wouldn't?)

UGM-73A Poseidon C-3

Start of Service: March 1971
End of Service: September 1992
Quantity Built: About 620

Missile Length: 409.2”
Missile Diameter: 74”
Missile Weight: 65,000 lbs

Propellant/Casing (Second Stage): Composite double base propellant in fiberglass/epoxy motor casing.
Propellant/Casing (First Stage): Composite double base propellant in fiberglass/epoxy motor casing.

Warhead/Range Combo 1: 14 x Mk 3 RVs with W68 (50 kiloton) warheads to 1,800 nm; with virtually no cross-range.
Warhead/Range Combo 2: 10 x Mk 3 RVs with W68 (50 kiloton) warheads to 2,500 nm; with 150 nm cross-range.
Warhead/Range Combo 3: 6 x Mk 3 RVs with W68 (50 kiloton) warheads to 3,000 nm; with 300 nm cross-range.
CEP: 550 meters (1,800 feet)

Note: The Poiseidon's Post-Boost Control System (PBCS) consists of a solid-fueled “gas generator” which when ignited, burns continuously, generating gas which is bled off to eight pairs of nozzles. Each nozzle has a valve which is opened or closed to control thrust, on instructions from the PBCS' guidance computer. This unusual and complicated system was chosen over the simpler hypergolic system used by the US Air Force, due to US Navy concerns over introducing liquid propellants into a submarine-based system.

During development, one of the main concerns was over Soviet ABM. In the end, it was decided to counter ABM by installing “Armed Decoys” or in other words, large numbers of small warheads; each hardened to a very high level to guard against enhanced radiation weapons (see Mk 3 RV entry). It was felt that as Soviet ASW became more effective over time, the large numbers of warheads initially loaded onto Poseidons could be downloaded to add more range, and thus area for the SSBNs to hide in.

UGM-96A Trident I C-4

Start of Service: 20 October 1979
End of Service: 2007

Missile Length: 409.2”
Missile Diameter: 74”
Missile Weight: 73,000 lbs

Number of Stages: 3

Propellant/Casing: Kevlar/Epoxy Motor Casing containing XLDB-70: Cross-Linked Double Base Propellant containing HMX, aluminum and ammonium perchlorate. Binders were Polyglycol Adipate (PGA), Nitrocellulose (NC), Nitroglycerine (NO), and Hexadiisocryanate (HDI)

Warhead Bus Material: Graphite/Epoxy
Warhead/Range: 8 x Mk 4 RVs with W76 (100 kiloton) warheads to 4,000 nm?
CEP: 222 to 463 meters

RV Deployment: After separation from the third stage, the warhead bus positions itself to take stellar sightings to update its guidance systems. Upon completion of this, the warhead bus swings over and flies backwards, with the RVs facing aft. When the correct velocity and position in space for RV release are reached, the RV is released from the warhead bus; which backs off and moves to another position for future RV drops. During this “back-off” maneuver, the vernier thrusters on the warhead bus impinge on the RVs, causing additional thrust to be imparted to the RVs, increasing CEP.

Notes: Was designed to fit within existing Poseidon missile tubes; and during development, the following specifications were laid down: It had to be as accurate at 4,000 nm as Poiseidon at 2,000 nm; and that the Trident Submarine Navigational System had to operate for up to 30 days without external input. One of the methods by which additional range was achieved was by a deployable aerospike, which reduced the frontal drag of the missile by about 50%.

UGM-133A Trident II D-5

Start of Service: March 1990

Missile Length: 534.6”
Missile Diameter: 83”
Missile Weight: 130,000 lbs

Propellant/Casing (Third Stage): Graphite/Epoxy Motor Casing. Burns for 40 seconds.
Propellant/Casing (Second Stage): Graphite/Epoxy Motor Casing containing NEPE-75. Burns for 65 Seconds
Propellant/Casing (First Stage): Graphite/Epoxy Motor Casing containing NEPE-75. Burns for 65 Seconds

Warhead/Range Combo 1: 14 x RVs to unknown range
Warhead/Range Combo 2: 6 x Mk 5 RVs with W88 (475 kiloton) warheads to 6,000 nm?
Warhead/Range Combo 3: 6 x Mk 4 RVs with W76 (100 kiloton) warheads to 6,000 nm?
CEP: 111 meters (90m with GPS updates)

Notes: After separation from the third stage, the warhead bus positions itself to take stellar sightings to update its guidance systems. Upon completion of this, the warhead bus swings over and flies backwards, with the RVs facing aft. When the correct velocity and position in space for RV release are reached, the RV is released from the warhead bus; which backs off and moves to another position for future RV drops. The software for the bus has been modified over that used for Trident I; in that the software will prevent the firing of any vernier thruster that might impinge on a RV until the RV is safely out of range of the gas plume from the vernier thruster. This increases accuracy; though it does slow down the rate of RV release.

Note II: The footprint of the Trident II's MIRV Bus is 3 times smaller than Peacekeeper's footprint, due to the solid fuelled PBCS.

Re-Entry Vehicles

Polaris Mark 2 RV

Heatshield: Nylon-Phenolic Ablative Material
Main Body Material: Aluminum

Poseidon Mark 3 RV

Manufacturer: Lockheed
Nosetip Material: Ablative Graphite
Heatshield: Beryllium
Main Body Material: Unknown

Notes: Had a shell designed to provide protection from X-Rays from ABM nuclear initiations. Supposedly, the Mk 3 is four times harder against radiation than any RV developed before or since.

Trident Mark 4 RV

Manufacturer: Lockheed
Nosetip Material: Boron Carbide-coated Graphite
Heatshield: Tape-Wrapped Carbon Phenolic (TWCP) Ablative
Main Body Material: Thin-Wall Aluminum Substrate
Ballistic Coefficient: About 1,800 lb/ft²

Trident Mark 5 RV

Manufacturer: General Electric
Nosetip Material: Metalled center “plug”, with Carbon/Carbon material forming the rest of the tip.

Mk 500 Evader

Note: Aeroballistic Re-entry vehicle which can perform pre-selected “canned” evasive maneuvers. Atmospheric maneuvering is carried out via the nosetip being “bent”, causing unbalanced aerodynamic loads. This is countered by shifting the electronics package around within the RV, enabling it to fly a controlled flight trajectory. Was flight tested five times on Minuteman I boosters between March 1975 and January 1976. A final test was then carried out with a Trident C-4 missile in June 1977, demonstrating compatibility.