About 25 years ago I was at a Naval Air show near my house.  The same base also had a squadron of ANG A-10 Warthogs which were also on display.  A group of us were talking to one of the A-10 pilots and someone asked him why they had the 30mm cannon as an anti-tank weapon, why wouldn't he want to use an anti-tank missile instead.  The pilot responded that they used both against tanks, but that there was a big advantage when using the gun while engaging SAM batteries.  The bullets from the gun were much faster than the SAMs.  So, if they did a pop-up maneuver, there was an excellent chance that they could destroy the missile control van before it would have a chance to lock on the A-10.

His point was that guns are nice, missiles are nice, but what's really nice is having both as it gives you more options.

Precisely.

A modern Infantry platoon has rifles, machineguns, grenade launchers and anti-tank weapons because the rifle can't do it all in the normal spectrum of combat.

A modern warship needs a mixture of offensive missiles, defensive missiles, offensive guns, defensive guns and anti-submarine weapons. Each helps in circumstances where one of the other weapons is not ideal. 

I expect, if and when there is an actual fleet versus fleet action between top tier peer naval forces, we will see several large volleys of anti-ship missiles fired.  Most of these missiles will be diverted via ECM or shot down via defensive systems, but more than a few will strike home.    The surviving ships, now that missiles are expended, will have the choice of pushing forward into gun range or departing the battle.  A ship with even a 57mm can at least continue the fight in these circumstances, whereas one with only CIWS cannot.  Those rare ships with 4 to 5 inch pieces will have a distinct advantage. 

Jeff (Jefffar) said:

I expect, if and when there is an actual fleet versus fleet action between top tier peer naval forces, we will see several large volleys of anti-ship missiles fired.  Most of these missiles will be diverted via ECM or shot down via defensive systems, but more than a few will strike home.    The surviving ships, now that missiles are expended, will have the choice of pushing forward into gun range or departing the battle.  A ship with even a 57mm can at least continue the fight in these circumstances, whereas one with only CIWS cannot.  Those rare ships with 4 to 5 inch pieces will have a distinct advantage. 

Except that they are hundreds of km apart and have a speed difference of a few knots at best. Guns are awesome, but they are not in any way comparable to ASM. 

Red7272 said:

Except that they are hundreds of km apart and have a speed difference of a few knots at best. Guns are awesome, but they are not in any way comparable to ASM. 

I'm not saying they are comparable.  The fact that they aren't comparable is what makes them useful.  When the AShMs are jammed/shot down/expended then a ship with a good gun is in a better position than a ship with weak or no guns. 

We haven't seen a real fleet battle between peer adversaries in 75 years. We know AShMs are great against individual ships, but we haven't seen what happens when two fleets equipped with high end CIWS, ECM, SAMs and AShMs go head to head.   I fully expect that when the missiles are done, there's still going to be ships from both sides. 

Jeff (Jefffar) said:

We haven't seen a real fleet battle between peer adversaries in 75 years. We know AShMs are great against individual ships, but we haven't seen what happens when two fleets equipped with high end CIWS, ECM, SAMs and AShMs go head to head.   I fully expect that when the missiles are done, there's still going to be ships from both sides. 

Ships don't fight to the death, they fight for objectives. Defend a convoy, defend against a landing, or occasionally destroy the enemy's warships. They will meet, fight and then run away trying to avoid enemy air and submarines. Damaged ships withdraw to port  for repairs and the undamaged underway replenish their ammunition fuel and stores. Same as it's always been. 

Jeff (Jefffar) said:

I'm not saying they are comparable.  The fact that they aren't comparable is what makes them useful.  When the AShMs are jammed/shot down/expended then a ship with a good gun is in a better position than a ship with weak or no guns.  We haven't seen a real fleet battle between peer adversaries in 75 years. We know AShMs are great against individual ships, but we haven't seen what happens when two fleets equipped with high end CIWS, ECM, SAMs and AShMs go head to head.   I fully expect that when the missiles are done, there's still going to be ships from both sides. 

Thats certainly possible. 

Its just that, after Day 1 of the War, we would expect enemy warships to fire at each other as soon as they are within missile / attack aircraft range. 

Modern Anti Ship missiles have a 500-1600km range. 

A 127mm/5" has a range of 37km. 

It seems kinda crazy to imagine that after both warships survive a mutual long range missile attack, they're then going to sail 500-1600km, essentially unarmed, to then try and finish each other off with their 5" pop guns. 

It would probably be more prudent to instead sail that 500-1600km to a friendly base to be rearmed. 

What needs to be borne in mind is that actual performance does not necessarily match up with what the fancy presentations suggest. The gap between theory and practice is liable to trip up over human factors.

A note I put together about the performance of Phalanx:

Anti-ship missiles have been fired at Phalanx-equipped ships on only a handful of occasions. On 17 May 1987, the destroyer USS Stark was hit by two Exocet missiles while patrolling in the Persian Gulf; the Phalanx system was not switched on. On 14 July 2006 the Israeli corvette INS Hanit was hit by a missile. Again, the Phalanx system was not switched on. In February 1991 during the Persian Gulf War an Iraqi Silkworm missile was fired at the battleship USS Missouri, which was being escorted by HMS London and HMS Gloucester (both Type 42 destroyers carrying Sea Dart). The missile was destroyed by a Sea Dart fired from Gloucester, the first time a SAM had successfully engaged an enemy missile during combat at sea. The Missouri did have Phalanx systems but these did not engage as the missile was destroyed before getting close. A few weeks later, Missouri was involved in another incident in which a (mistaken) warning of a missile attack was given. The Phalanx system of the escorting frigate USS Jarrett was switched on, and fired at defensive chaff launched by Missouri.

As tech progreses and programambe and even guided rounds are becoming a norm the gun is far more versatile than ever

I particularly like how Italians chose to have 2x 76/62 mm Super Rapid guns on their STOVL carrier .

Russian AU220 naval munt with 'stealth garage' , 5T total weight

Thought this might be relevant.

L3 / DARPA have developed and plan to field a guided 57mm shell. This would be employed on the new FGGX Frigate and LCS.

https://www.navalnews.com/naval-news/2019/07/video-darpa-mad-fires-anti-ship-missile-self-defense-for-lcs-ffgx/

https://www.upi.com/Defense-News/2019/05/28/L3-awarded-92M-to-support-Navys-57mm-HE-4G-ammunition/3631559049733/

https://www.youtube.com/watch?v=vY9rJBL1S2Y

This would give the 57mm potential capability against UAS and missiles, and a very good capability against rapidly moving small boats.

If effective, this would prove a very useful Naval Gun indeed. 

Then add in work on 76 and 127mm rounds of similar capabilities, and we'll have naval artillery for a long, long time.