They are a UK AA gun.  It looks like a bunch of AAW shooting really fast and making a rrrrrrrrrrrrrrrrrr noise.

In components its the one all the way at the bottom.  Its the septuple barrel with .52 reload. 

manchine AA gun?

Pom Poms are the nickname given to the 1.57" Mark 8 AA guns at lvl 45.

http://trainworld.us/NF2/AA_Gun/AA_HMS.html 

UK Pom Poms are the fast firing, low damage anti-aircraft gun used by most RN players as AA. They have a very steep golden angle at around 51~52 degrees, making them perfect to counter the diving bombers. 

Don't rely on them, they're notorious for jamming. The game. When ~5 players start hammering the skies.

Also, they're useless against ships unlike the 20mm of the German U-Flak, which has the same sprite. 

They are only usable by the UK AA gunners classed above level 45. And makes a terrific noise that sounds very similar to a fully automatic rifle.