Naval News reports,

The Pakistan Navy has commissioned its first Offshore Patrol Vessel (OPV) 2600, named PNS HUNAIN, at Constanta Port in Romania.

This is a rare beast, a heavily armed Offshore Patrol Vessel. It is a medium sized OPV, little more than half the size of a National Security Cutter or Offshore Patrol Cutter:

• Length: 98.0 m (321′)
• Beam: 14.6 m (48′)
• Draught: 4.0 m (13′)
• Displacement: 2600 tons
• Speed: 24 knots

The basic design, the DAMEN OPV 2600, may have been the Bollinger proposal for the Offshore Patrol Cutter competition. At that time DAMEN’s generic OPV 2600 looked like this.

OPV 2600 multi-mission patrol vessel rendering (Source: Damen)

The ship has not been fitted out yet. If the model seen in the report is actually the way the ship is equipped, the Pakistani OPV will have

• four launchers for Pakistani Harbah anti-ship cruise missiles. 
• twelve VLS for 40km range cold launch Albatros NG (Sea Ceptor/CAMM ER)
• one Leonardo OTO-Marlin 40mm
• one Turkish built 35mm CIWS
• two Turkish Aselsan “SMASH” 30mm remote weapon stations.
• two Aselsan STAMP remote .50 caliber remote weapon stations

Pakistan seems to have decided it was better to go with a small 40mm gun rather than a 76mm to make room for the air defense missiles. I think that was a good decision and may save money in the long run.

My own feeling is that the only thing guns can do that missiles cannot do as well or better is fire shots across the bow. To be able to fire a shot across the bow is a requirement for a law enforcement vessel, but while it is commonly done in the CG by a .50 caliber, if you want to do it at a greater range, say four km or about two nautical miles, the 40mm is a good choice. The need for a larger gun for that purpose is highly unlikely.

Upfront costs to buy a medium caliber gun, its fire control systems, and its initial ammunition allowance are high, as are long term personnel support costs.

A capability to launch missiles that have a higher probability of hit and greater hitting power beyond the effective range of 57 or 76mm guns may actually be relatively inexpensive. Plus, VLS missile launchers may actually look less intimidating than heavy guns.

Graphic from Leonardo