Herring is a light scout/AA ship, offering very high speed, and a big line of sight. Use them in the beginning of sea battles in order to harass enemy’s early base structures and block constructors from expanding. 

Their AA turret is weak and won’t stand a chance versus more advanced aircrafts but during the T1 stage it proves very useful to protect your ships from EMP drones and gunships. Always include a bunch of these in your fleet.

They are hopeless in a matchup with any other ships, hence only use them as a support/scouting force. 

Herrings are a bit slower than their ARMADA counterpart (Skater).