Experts Question US Navy's Decision To Swap Out DDG 1000's Secondary Gun (DefenseNews)

This is exemplified in the CMANO scenario "Op Brass Drum" when a Zumwalt, a Burke and two LCS are set upon by 'pop up' threats posed by Iranian fast attack craft.

 

The realism of the teleport appearance of the Iranian threat aside, the 57mm does help to keep the attackers at bay (not quite a swarm) and if they are in 30mm range, you are likely going to get hurt.

 

Even so, you find yourself wanting much more than the 57mm and God help you if a real "swarm" suddenly appeared.

CMANO inherits Harpoon 3 impossibility to fix a percentage of apparition of platforms on scenarios. It's very difficult for me to think on this parameters to design scenarios.

CMANO inherits Harpoon 3 impossibility to fix a percentage of apparition of platforms on scenarios. It's very difficult for me to think on this parameters to design scenarios.

 

Well, CMANO inherits more than a few of Harpoon's limitations, imho, but that aside ... what about the 57mm vs 30mm?

http://navweaps.com/Weapons/WNSweden_57-70_mk123.htm

 

57mm Mk3: 220 r/m, 2,4 Kg shell weight (3P), 1035 m/s muzzle speed (3P), 200 rounds in mount, 200 in total?

range at 45º = 7,45 nm (HE)

AA ceiling = 7600 m/4,10 nm, barrel elevation 77º maximum.

Shell weight at 10 seconds burst = 36,66 rounds x 2,5 Kg = 88 Kg.

 

http://navweaps.com/Weapons/WNUS_30mm_BushmasterII.htm

 

30mm Mk46 Mod 1: 250 r/m, 0,425 Kg shot weight (API-T), 983 m/s muzzle speed (APFSDS-T), 200 rounds in mount.

range = effective 1,08 nm, máximum 1,629 nm

AA ceiling = N/A, but barrel elevation only 45º máximum (AA ceiling perhaps only some 1659 meters/0,896 nm)

Shot weight at 10 seconds burst = 41,66 rounds x 0,425 Kg = 17,70 Kg.

In conclusion:

- By shell weight in 10 seconds burst 57mm wins almost 5 to 1 (88 Kg/17,70 Kg=4,95).

- By range (máximum) 57mm wins almost 5 to 1 (7,45 nm / 1,629 nm = 4,57).

- By máximum AA ceiling 57mm wins almost 5 to 1 (4,10 nm / 0,896 nm = 4,57).

- By rounds per minute 30mm wins 1,13 to 1 (250 rpm / 220 rpm = 1,13), very scarce advantage counting the other parameters.

 

Magazine ammo capacity aside, considering the same accuracy in both guns, against a boat swarm the very slightly advantage in rounds per minute of the 30mm can't compensate the short range of 30mm.

 

I will look for effective ranges for best comparison.

Supposing the boat of a swarm sails at 40 knots and is approaching a USN ship to impact his suicide explosive charge against her hull sides:

40nm travelled in 3600 seconds (1 hour).

57mm range at 45º = 7,45 nm , crossed at 40 knots in 670,5 seconds (11,17 minutes) of exposure to 57 mm fire, 2457 shots theorically fired (but remember ammo magazine capacity only some 1200 rounds).

30mm range at 45º = 1,629 nm , crossed at 40 knots in 146,61 seconds (2,44 minutes) of exposure to 30mm fire, 610 shots theorically fired (and probably much more in magazine).

 

As side conclusion, the probability of 57mm gun of stop a swarm should be about the double of the probability to stop the swarm of the 30mm gun (1200 shots fired /610 shots fired =1,96).

Heh, great analysis, Enrique.

 

Certainly leans in the direction of weight concerns and top heaviness being the real concerns behind the switch.