The grate is part of the helicopter winch down system. Lets them operate in higher sea states than if they tried to land normally.
Confirmed, this is the real case of that roaster.
In the Dutch navy the Heli's have an hook wich can be attached...
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Fryssian AU with Lt.Maverick 114
viewtopic.php?f=14&t=9802&p=193331#p193331
Embarked on: HNLMS Karel Doorman A833
To do list:
-Zeven Provincien class cruiser
-Joint support ship all sides
-F124 Sachsen class frigate
-F125 Baden-Württemberg class frigate
-Clemencau class aircraft carrier
-Zeven provincien class frigate
-Poolster class AOR
-Amsterdam class AOR
-Minas Gerais aircraft carrier