DD-998 USS Towers (2000)
22ft draft at ~9860 long ton full load (26ft navigational)
The SC-21 Cost and Operational Evaluation Analysis (COEA) faced a problem, and with it an opportunity: the
US Navy was aging, but the aging units constituted the wrong navy.
As the Spruance-class destroyers and Perry-class frigates approached block obsolescence in the 1990s, it was
clear that neither was especially well suited to the post-Cold War US Navy emphasis on littoral and land strike
operations. It appeared as though the light-duty AAW of the Perry could be combined with the strike and sea
control capability of the Spruance in a single platform. Certainly the new Flight IIA Burke met these needs,
and every other, and a navy structured entirely around these ships surely satisfied every admiral's dreams.
However, it was clear that Burkes were unaffordable in the numbers needed.
Operations in the Gulf had also demonstrated the utility of low-observable ("stealth") platforms. The Burkes
were designed with some low-cost and low-impact LO features, but a whole new hull would be required to achieve
what some thought desirable. The COEA effort considered a range of stealthiness, and with it a range of cost
and ship impact: everything from a cheapened Burke to the recently declassified Sea Shadow, the latter almost
unrecognizable as a ship.
The Towers class that emerged from the COEA studies represented a sensible middle ground in most respects.
Effective sensors, but not the best. Efficient and high-tech machinery plant, but not the most efficient or most
high-tech. Powerful armament, but not the most powerful. Spacious enough for future refit, but not colossally
over-sized. Survivable, but not indestructible. And stealthy, but not outrageously stealthy. Indeed, in this final
characteristic she closely resembles the French La Fayette frigates that recently entered service.
The Towers destroyers may completely extirpate the destroyer escort/frigate categories in the Naval Vehicle
Register. Only time will tell whether less-capable variants, or follow-ons, to the Towers-class introduce a new
categorical division. The Towers are also designed with an Aegis half-sister in mind, in light of the very positive
experience with the Spruance-derived Ticonderoga.
As so much on this ship is hidden, rather than a list of characteristics, the reader will be taken on a guided
tour of the ship's profile that may explain many of the choices and considerations that led to this final design.
The "chapters" [i.e., (1), (2)] are not listed compartment-by-compartment, and are merely intended to
break up the flow of prose.
At the bow, we find very little of the regular deck gear that would be equally familiar to a sailor of a Burke or a
battleship. Aside from a protruding prow anchor, nearly everything (bollards, windlasses, and all) lies hidden
below deck (the second anchor, like a submarine's, emerges from the keel). As designed, a flag/light pole and
clip-your-harness life rails were the only surface clutter. These latter fell under immediate criticism; the forward
UNREP spot and non-skid surface (!) clearly meant that sailors were intended to work on the exposed bow in a
seaway. The low-observable angled composite helo nets were adapted to the bow of the first unit before
she had even completed builder's trials. These collapse down onto the deck when not in use.
Below the water, the Towers class demonstrates her first concession to economy. The new-style bow dome on
Towers herself contains the familiar SQS-53C low-frequency sonar that can trace its heritage back to the 1960s.
Her sisters... it depends. To fill out the force structure, some units may instead employ the DE-1160C, an
upgraded version of the much-derided SQS-56. Later units may make use of the product of Northrup
Grumman's 21HS program, if that is seen to its conclusion.
A Towers-class destroyer is separated by four 1m cofferdams into four large and one small units
(subdivided, of course, into smaller watertight compartments). Aft of the bow compartment
is the first of these cofferdams. For survivability, each large unit (that is, not including the bow compartment)
contains at least emergency power generation for electricity and ownship-powered pumping.
Making our way aft, the familiar 5"/54 gun is absent. In its place is a Mk 110 57mm/70. This is a popular
utility mount the world over, and acts as a CIWS for the class, but for NGFS it serves little purpose. The
explanation will soon be clear. Aft of the gun is an OE-538/BRC submarine-derived multifunction communications
mast. Its purpose on this class is to fill blind arcs (HF) and serve as backup (VHF/UHF); it is not the primary
radio system. The weather deck (at the bow, 01) drops down from the shell of the ship around the
forward Mk 110, and bulwarks aft of this point provide for more regular operation and positive crew protection.
Aft of the 57mm and OE-538, we find a 64 cell Mk 41 strike-length VLS, concealed from view as on the British
Type 23. With the recent adoption of the four-pack Evolved Sea Sparrow Missile, this is a deep enough magazine
for the whole ship. There is only one other missile launchers aboard; even Harpoon is VLS on this hull [ed: VLS
Harpoon was live-fire tested]. The ship's combat system supports the Standard missile, but cannot illuminate
beyond MR range. ER missiles are theoretically supported with CEC, but they are generally not carried. Below
the VLS is a medium-sized fuel tank used in part for pitch control, a Caterpillar C32 900kW emergency diesel
generator, and a Thrustmaster TH1000MLR retractable electric azimuth thruster (800kW).
Next we find the "real" gun aboard: the twin 155mm VGAS (Vertical Gun for Advanced Ships). VGAS keeps
the heavy parts of the gun low in the ship, and it minimizes blast concerns, but (of course) it cannot be trained
and aimed. It is thus limited to firing guided projectiles. Surprisingly, giving up aiming reduces range only
slightly; the ideal elevation for this rocket-assisted ammunition is in excess of eighty degrees. The overriding
concern for this ammunition is to get out of the thick, draggy lower atmosphere.
Atop the VGAS is a bolt-on/crane-off structure for deck gear, roughly akin to a pair of 20ft shipping containers
(although much sleeker). This deckhouse contains firefighting equipment, safety gear, and all of the other deck
gear necessary for operating a ship from day to day.
Aft of the VGAS compartment is the second cofferdam.
The next compartment is, by a wide margin, the most complicated and expensive. Down at the third platform,
an auxiliary machine room provides all of the chilled water the crew and equipment could desire; the Towers
class is as nearly as possible fully water-chilled to reduce the infrared signature of hot-air plumes, and operations
in the Gulf have demonstrated the utility of excess AC capacity for both crew comfort and electronics uptime.
There is some concern that these units may suffer from excessive steady roll from windage; space and volume
is reserved for fin stabilizers for later units at the third platform in this compartment if the roll is intolerable.
The CIC is on the first platform, insulated from fore-to-aft foot traffic. At the 03 level we find the pilothouse,
chart room, and CO's sea cabin.
At 04, we find more concession to cost. On a new DDG or CG you would likely find flush-mount ESM/ECM
arrays, active-array SPY-1, and more. The Towers are more modest. ECM is the same familiar SLQ-32(V)5,
here enclosed in radar-transparent composite boxes. The inherit boxiness and radar signature of SLQ-32 is
accepted, with some attention from radar-absorbing materials. The enclosure merely exists to prevent corner
reflectors from the structure above the SLQ-32.
The radar at this level is not the 12ft array of SPY-1, but an enlarged version of APG-77, the X-band search
and fire control radar of the F-22. The F-22 array is around 3ft in diameter; the arrays on a Towers are 4.5ft
high and 3.5ft wide, angled at 60deg to the ship centerline. This radar is used for fire control, target illumination,
AA gunfire support, rapid-refresh horizon surveillance, and heightfinding.
Somewhat paradoxically, these highly advanced radars actually reduce the required processing power
of the combat system. X-band is much inferior to S-band for volume search. As such, the APG-77 arrays
fail to see many of the real (and many spurious) contacts that SPY-1 might detect. "Real" targets will be
detected by other sensors, and APG-77 mostly tracks queued targets. The Towers thus possess a highly
effective local-defense combat system, but they are not area-defense workhorses like an Aegis destroyer
or cruiser. Sponsoned off of the front of this level of the deckhouse is are domed SATCOM antennas supporting
WSC-3 (UHF Follow On (UFO) constellation and future Mobile User Objective System (MUOS) constellation, to
port) and USC-38(V)2 (MILSTAR EHF constellation, starboard of the centerline)
05 features 4ft WSC-6(V)X SATCOM antennas on each beam, supporting the DSCS and future Wideband
Global SATCOM SHF constellations. Forward of these is a SPS-64(V)9 X-band navigation radar. Above these
towers an enclosed sensor/mast structure resembling the one tested on Radford in the late 1990s in the
AEM/S program. This composite structure is transparent to RF energy at UHF frequencies and lower, and
opaque (reflective) to higher frequencies.
The lowest level of the mast contains air ducts that serve a fan room on the 04 level. Above this is an
enclosure for the venerable SPS-49, the primary air search sensor aboard. The mast is lowered onto the
ship after SPS-49 is installed. The mast is sized to support either the standard parabolic antenna or the
planar array tested on Leyte Gulf in the 1990s, which (if purchased) will offer intrinsic L-band heightfinding.
This installation has the virtue of preserving some manner of frequency diversity within task groups; an
arbitrarily powerful S-band jammer could render a dozen Burkes valueless. Inclusion of L-band equipment
forces the adversary to jam search radars in multiple bands.
Above SPS-49, the corners of the mast are separated off from each other (and from SPS-49) by
RF-opaque bulkheads. Forward-port and rear-starboard are AS-3506/SRD-19 arrays for Classic Outboard,
for communications-band direction-finding and intelligence collection. Forward-starboard and rear-port
are the familiar "lampshade" arrays for Link 16 and Cooperative Engagement Capability. The RF-opaque
bulkheads prevent these various arrays from interfering with each other. This arrangement explains the
somewhat ungainly rectangular AEM/S compared to the testbed on Radford.
At the tips of the rough diamond formed by the interior bulkheads are navigation lights, a laser warner, a
COTS-derived digital video camera providing situational awareness (the first units went to sea with the
Canon XL1, known to the public as the video camera flown aboard the Space Shuttle), and SLQ-XX,
presented at Navy League 1995 as the "LAMPS III Block II interferometer array".
The topmost enclosed level of the AEM/S contains SPS-77, the US version of the Saab Sea Giraffe AMB
C-band 3D multifunction radar. This offers surface search and supplemental air search capability.
Note that only the low-elevation (0-8deg) and medium-elevation (0-25deg) modes are supported,
because higher beams would strike the ceiling of the AEN/S. This represents another concession to cost;
Towers-class destroyers rely on mod-APG-77 for zenith search at high elevations. SPS-77 offers sufficient
precision that it will be able to directly designate targets to the eventual Block II (active-seeker) ESSM.
C-band search also offers further frequency diversity, although SPS-77 is insufficient to wholly cover
a task group.
On the roof of the AEM/S, the Towers class mounts the primary antenna for the ARQ-59 Hawklink data
link. Sponsoned forward is a SPS-55 X-band surface search antenna (contained, in this installation, within
a low-observable angled cover). Aft is another SPS-64(V)9, and to either side are sponsons for anti-collision
lights, weather sensors, and flag lines. Above the Hawklink antenna is another higher mast. Sponsoned
forward from this mast is a SAY-1 TISS thermal imager, camera, and laser rangefinder. Above the TISS
is a multifunction VHF/UHF communications mast identical to the one tested on Radford. This is
surmounted with TACAN.
The next compartment aft is the #1 main machinery room. This represents another innovation on
the Towers class. Many COEA proposals featured fully-integrated electric propulsion, so that the fewest
possible prime movers could operate at once. At a bare minimum, an underway Burke (or any other
US gas turbine ship) must turn two turbines: one power turbine and one ship-service gas turbine
generator. Even this most efficient mode requires the ship to trail a shaft.
The Towers do not feature full IEP, but they derive many of the benefits with a partial COGLAG
arrangement. Each MMR contains two LM2500 (25,000shp, 18.6MW) feeding into the main reduction
gear, just like a Burke. However, the gearbox is also directly connected to a 6MW motor/generator
operating on ship voltage and frequency. The final powerplant component in each MMR is a 3MW
AG9140 SSGTG. The MMRs also contain fan rooms that serve the internal spaces, plumbed off of
the main gas turbine intakes (unfortunately, the shape of these intakes requires some internal
disassembly to access the main gas turbines through their bolted removal plates on 02 level).
This arrangement provides unmatched operational flexibility.
Gas turbines can be mixed and matched to operate at many plant power levels while running all
turbines at maximum power. Roughly speaking, such available power levels (combined hotel and
propulsion) are 3N+18.6M MW, N=0..2 and M=0..4, a total of 15 combinations spanning 3MW to
80.4MW. Total electrical generation capacity is 18MW, which may support future directed energy
In other words, at lowest duty (at anchor, or transiting harbor), a Towers can operate on one or two
SSGTGs (or, for that matter, a C32 diesel generator), operating at peak power and efficiency.
Underway, a Towers can operate on both SSGTGs, or a single LM2500 providing power to both
shafts and to the ship's hotel loads. At medium power, with both shafts powered directly by lit
LM2500s, the SSGTGs are often redundant, and can be left cold or available for maintenance.
MMR1 serves the port shaft and exhausts out of a port-side uptake with a AS-5085 HF receive
antenna bracketed off of the front (this also holds the ship's bell). To starboard on the weather
deck, another AS-5085 transmits in HF, and an INMARSAT antenna is provided. Three Mark 7
25-man liferafts make up the starboard bulwark aft of the bridge wing (the liferaft outfit supports
a potential complement of 325 crew, although of this, a substantial reserve is maintained for an
aviation detachment, special forces, and/or VBSS). On the main deck is the ship's boat bay, with
an overhead crane and two Sea Force 900 RIBs. A cable slipway from the boat bay leads up to the
forward weather deck, for transfer of a sea painter outside the shell of the ship. The boat bay is
protected from RF intrusion by an arrangement of rod-stiffened fine-gauge chain that opens aft
for boat deployment. The life rafts are covered by similar chain.
Aft of MMR1, a short compartment contains one of the primary fuel tanks (located centrally to
minimize pitching). The main deck to port contains a Sea Force 490 RIB as the abandon-ship
boat. At 02 are four Mark 7 liferafts and four SRBOC decoy launchers. Between the SRBOC
launchers is a third SATCOM antenna for WSC-6(V)X, which covers the zenith over the ship.
Further aft is MMR2, serving the starboard shaft. This compartment is identical to MMR1 except
that the large boat bay is replaced by a narrower bay for UNREP, similarly shielded, with the
balance of the compartment volume above the main deck made up of interior spaces. On the
weather deck are three Mark 7 and an enclosure for an 8-cell Mark 41 SDLS module, the first
VLS of this length in the US Navy. This launcher is exclusively for self-defense: Nulka, RAM,
and ESSM. On the MMR2 funnel is mounted an AS-1016 VHF antenna for ground force support.
Sponsoned off of the starboard side of the MMR2 compartment is another UHF SATCOM antenna.
Aft of MMR2 are two compartments that make up an auxiliary machinery room and an aft fuel
tank, both surmounted by the hangar. The Towers-class hangar is offset to port, with a clear
working area 48ft long, 40ft wide, and 20ft high. This suffices for two H-60-size helos, which
are served with a RAST recovery system on the flight deck. To starboard is a second UNREP
bay. At the forward end of these two compartments, four twin Mark 32 SVTT deploy Mk 50
torpedoes to port and starboard. These launchers also deploy a modified version of the
SLQ-49 "rubber duck" inflatable radar decoy. On the weather deck, there are three Mark 7
each to port and starboard.
On the aft end of this compartment is an additional deckhouse that mounts a second Mk 110
57mm gun. Atop this deckhouse is a third mod-APG-77, typically trained aft. However, this
radar is able to rotate through 360deg in the event that the systems in the AEM/S are rendered
inoperable by damage (this rotation is limited to +-180deg, not continuous). Atop this radar
is an AS-3512 VHF/UHF antenna for backup communications, as well as an omnidirectional
UHF SATCOM antenna. In concert with the SDLS VLS, the Towers can maintain a credible
AAW self-defense capability even if everything forward of MMR2 is non-functional, although
instantaneous search/track/target would be limited to a single 120deg sector. To starboard
of the deckhouse is a second Hawklink antenna to cover blind arcs. Sponsoned off of the back
of the hangar is the third WSC-3 UHF SATCOM antenna. On either beam are antennas for
The flight deck of the Towers class is large and strong enough to support every helicopter in
the US military except for the H-53E family, including the H-47 and V-22 families (although
these cannot be hangared). On the outside of the flight deck (and proceeding some distance
forward) are eight SRD-17 HF antennas on each beam, for skywave HF DF and single-station
location. Eight more SRD-17 antennas are arrayed across the stern. On the first platform is
a second C32 900kW diesel generator, exhausting through the starboard side of the hull just
below the waterline.
Below the waves, the Towers use a skeg hullform aft. This hullform allows the stern to
narrow as little as possible while maintaining good hydrodynamics. This allows the aft
location of the SRD-17 antennas with minimum computational expense. It also facilitates
easy docking. The screws are controllable and reversible, identical to those fitted to the
Burkes. Advanced pumpjet propulsors were investigated, but the low noise (for ASW) and
low-speed efficiency won the argument for this class.
Right aft, twin rudders provide directional control. The first platform contains line-handling
stations on either beam. At the fantail, SLQ-25 Nixie torpedo decoys deploy (to port)
and an SRQ-19 passive towed array is fitted (to starboard). Attempts were made to provide
weight and volume to fit a VDS if desired in the future.
The future of the Towers class is somewhat less certain than their scale and number might
imply. Though they retain weight and stability margins characteristic of the Spruances that
they replace, it remains to be seen how the increasingly integrated combat system and
even topside arrangement will be upgradable in service.
Though some suspect a cheeky character in NAVSEA used the class name to offer
commentary on the substantial AEM/S structure atop the pilothouse, the lead ship is named
after US Navy Admiral John Henry Towers (1885-1955), an early naval aviation pioneer (NC-3
crew member) and eventual DCINCPAC in the Second World War and CINCPAC immediately
Sorry for the novella. That was about as short as I could get it!
This was very fun. I'm glad to have had a chance to participate (work has been pretty crazy).
For those who didn't recognize it, this is sort of an outgrowth of COEA "Maritime Combatant"
I didn't want to just draw that
, so I had to make some further design
decisions and priorities to take it in my own direction
I don't think all of those decisions are
necessary fantastic, but overall I'm happy with how it came out.
Aegis'd DDG version to come, once the challenge and judging are over