Four years ago I wrote a post suggesting that the Offshore Patrol Cutter might be designed from the start for a wartime weapons fit, but then fit them out with only those systems required for their peacetime missions, which might have included only its helicopter, UAS, and 25 mm Mk38 Mod2 gun(s).
I started with the assumption that the OPC should be able to mount a weight of weapons at least equal to those mounted on the 255 foot Owasco class cutters as built during World War II (140-150 tons). This figure did not include ammunition other than depth charges, consequently, nearly all the weight was above the main deck. This now appears very conservative in that the Eastern OPC design is about twice the size of the Owasco Class. (For another data point, when built, the USS Fletcher, first of a class of 175 destroyers with a design displacement of 2,700 tons, had 161.8 tons of armaments and 190.8 tons of ammunition.)
In the earlier post, a possible wartime outfit that I believed might be used for designing the ship (and the weights I used) included:
- H-60 11 tons
- UAS (weight unknown, but an estimate probably on the high side)
- Mk 38 mod 2 25 mm guns (x2) (estimate on the high side) 3 tons
- AN/SQR-20 Multi-Function Towed Array (MFTA)(Thales CAPTAS 4) 20.6 tons
- Mk 32 Surface Vessel Torpedo Tubes (SVTT) (two triple and 12 torpedoes) 5.2 tons
- CIWS (2) (Phalanx, SeaRAM, or Mk 49 RAM launcher, probably Mk 49 fwd, SeaRAM aft) 14 tons
- 5″/62 Mk45 33 tons
- Mk 57 or Strike length Mk 41 Guided Missile Vertical Launch Systems (8 cells) 33.6 tons
Total 124.4 tons
Since we now have a notional design for the cutter and my own views have changed somewhat, I thought it might be worthwhile to revisit how this class might be armed in wartime. The design may have ruled out some of the systems above, but the surprisingly large size suggest it should be fairly adaptable.
In fact it looks like the OPC could be turned into a credible warship adding only deck mounted systems that require only minimal deck penetration for cabling and the like.
What’s already there?:
Based on earlier information, as built, the design will includes provision for
- an MH-60 helicopter (11.75 tons),
- a 57mm Mk110 gun plus 1,000 rounds of ammunition (15.4 tons total, 7.5 tons for the gun, 7.9 tons of ammunition),
- a 25mm Mk38 Mod2 gun (1.15 tons),
- a pair of Mk49 ROSAM mini-Typhoon remote weapon stations (pdf) (0.25 tons)
For a total of 28.55 tons
Anti-Ship Cruise Missile:
RGM-84 Harpoon SSM was fired from a Mk-141 missile launcher aboard USS Shiloh (CG 67). The Shiloh’s beam is only one foot more than that of the Offshore Patrol Cutter. Looking at the photo, you can see that the launchers take up well under half the width of the fantail.
Photo: Click to enlarge
Photo: Click to enlarge. The relatively small foot print of the Mk56 VLS system (pdf) can be seen here on a Danish Absalon-class command and support ship (beam 64 feet, by comparison the Offshore Patrol Cutters’ beam is 54 feet–same as that of the Bertholf class National Security Cutters). Two sets are visible in the foreground, one set of twelve with missile canisters with red tops in place to the right, on the ship’s centerline, and a second set of twelve without canisters to the left. The Absalon class has three twelve missile sets, with the third set off camera to the right.
Mk38 mod2/3 and Mk49 ROSAM:
I will assume that the two Mk49 RO
SAM will be retained and the Mk38 mod2 (or mod3) will be relocated and a second Mk38 (1.15 tons) will be added.
The resulting additions would be:
- Multi-Function Array (CAPTAS-4) (20.6 tons)
- MH-60 (11.75 tons)
- 8 x LRASM (30 tons)
- 24 x ESSM (23 tons)
- 2 x SeaRAM (22 missiles) (17 tons)
- 57mm Mk110 gun w/1000 rounds (15.4 tons)
- 2 x Mk38 mod2/3 (2.3 tons)
- 2 x .50 cal. in Mk49 ROSAM (0.25 tons)
This totals 120.3 tons or 91.75 tons more than the planned outfit as built.
We don’t really know if the ship can take this much weight. Assuming it displaces 4,000 tons, which seems likely, this is about a 2.3% increase in displacement and much of the weight is relatively high.
Is it feasible?
There are things that can be done to counterbalance the effects of this additional weight. Some fuel tanks might have to be left permanently full or be converted to ballast tanks. Given the extreme range of the cutter, even half of the design range would be more range than most Navy combatants.
We know the ship is supposed to have some weight moment reservation for additional weapons but we don’t know how much. There is also the requirement that the ship be able to take on, feed and shelter 500 migrants on the foc’sle or flight deck. Those 500 people alone would amount to almost 40 tons of additional top weight.
There are alternatives that could provide a simlar outfit while moving the weight lower. A more extreme change would be to replace both the Mk56 VLS (23 tons) and the 57mm Mk110 (15.4 tons) with Mk41 VLS (33.6 tons) in place of the 57mm. We would loose the gun, but this would provide the additional capability of launching Anti-Submarine Rockets (ASROC) as well. That might be a good trade, but it would require more radical reconstruction.
In short, adding less weight in weapons than carried by the 255 foot Owasco Class cutters of WWII, the Offshore Patrol Cutter could be turned into an effect surface combatant comparable to many frigates. The same sort of alterations could also be appied to the National Security Cutters.