Question: Why is the 16 SLBM SSBN-X larger than a 24 SLBM Ohio? (see Table way below. Displacement and Beam is larger).
The larger the submarine the smaller the influence of its weapons on displacement and length.
The displacement of the future SSBN-X's 8 fewer SLBMs (16) than the Ohio’s 24 and dimensions for 8 fewer tubes doesn’t mean the SSBN-X is 33% less in displacement/length/beam.
- Beam always needs to be the same or greater to accommodate the length of the
SLBMs.
- The Ohio’s 24 SLBMs were a break in the decades old pattern (page 36) of 16 SLBMs.
- The most pessimistic predictions (of many opposing Russian SSBNs) didn't
materialise. (see comparative Table below).
- The USN must be calculating that threat, stealth and budget means 12 x 16 SLBM
SSBNs is adequate for the 2030-2080 SSBN-X era.
- But more Common Missile Compartment (CMC) quad-packs and more MIRVs
per SLBM can always be retrofitted if need be.
The SSBN-X crew (at 155) remains the same because all the requirements needed to maintain the submarine and its SLBM payload involve the same crew specialities, damage control and other fixtures for 16 as they do for 24. There may even be a need for a few more crew in, say 22 years time, to improve stealth.
- the task of safely operating the reactor requires many crew no matter how many missiles are carried
- the task of safely operating the reactor requires many crew no matter how many missiles are carried
An inbuilt capacity to absorb improvements and stealth over the 42 year life of SSBN-X involves room to grow into spaces left empty in the hull. Much of this is expanding the computer power by adding more memory and other processing on spare racks in the combat system database. See “must be fitted with the most up-to-date capabilities and stealth to ensure they are survivable throughout their full 40-year life span.”(# below), So more electronics and memory for future active stealth and combat system upgrades may take up much extra space-displacement.
Perhaps more decoys the size of HWT sized UUVs (if the 4 torpedo tubes are retained?).
The tubes for SSBN-X's SLBMs are the same 87-inch diameter as on the Ohio-class, but are a foot longer - leaving some margin for a future missile design. This explains the need for a space/displacement increasing Beam of 43 feet compared to the Ohio’s Beam of 42 feet.
The new reactor may be very slightly heavier and larger, with more 90+% HEU for the longer life between refuels (stretched from the Ohio's 19 year mid-life, to being sufficient for the SSBN-X’s whole 42 year service life).
SSBN-X and Ohio class Comparison Table
Measure/Replacement or Ohio | Ohio Replacement, SSBN-X, Columbia class | Ohio class |
Number of SLBMs | 16*** In Common Missile Compartment (CMC) quad packs # | 24* But just 20 after 2018* |
Launch tubes | Same 87 inches SLBM launch tubes *** | Same 87 inches SLBM launch tubes *** |
Length | 560 feet *** | 560 feet *** |
Beam | 43 feet *** | 42 feet *** |
Displacement | Larger, 20,815 tons “(as of August 2014)”submerged *** | Smaller, 18,750 tons submerged *** |
Crews Blue/Gold | 2 x 155 # | 2 x 155 |
Years between HEU refueling | 42 (service life) *** | About 19 * |
Drive, propulsion | electric-drive propulsion train *** pump jet, X-plane rudder# | mechanical-drive propulsion train*** bare propeller, cruciform-H rudder |
UK Successor and Vanguard classes | On UK Successor class 8 x Trident IIs, In Common Missile Compartment (CMC) quad packs # UK made warheads ** | UK Vanguard class carry 16 x Trident IIs, UK made warheads** |
* page 3 Ronald O'Rourke Specialist in Naval Affairs, Navy Ohio Replacement (SSBN[X]) Ballistic
Missile Submarine Program: Background and Issues for Congress, May 27, 2016
https://www.fas.org/sgp/crs/weapons/R41129.pdf(5 MB PDF)
Missile Submarine Program: Background and Issues for Congress, May 27, 2016
https://www.fas.org/sgp/crs/weapons/R41129.pdf(5 MB PDF)
For an even more up to date CRS report on the SSBN[X] see Ronald O'Rourke’s Navy Columbia Class (Ohio Replacement) Ballistic Missile Submarine (SSBN[X]) Program: Background and Issues for Congress, of August 18, 2016 CRS 7-5700 www.crs.gov R41129 https://news.usni.org/wp-content/uploads/2016/08/R41129-1.pdf . This August 18, 2016 Report was not publically available when I wrote the Submarine Matters article above.
Pete