The requirements are:
Maxed Viking
It is also recommended:
Maxed Delta
Maxed Poseidon
Maxed Shipyard
Rank is 15 or higher
It can also be useful to have:
Maxed Walls
Maxed Rocket Tower
Maxed Torpedo Platform
The first step is to directly go for HQ3 while not neglecting economy as described in Build Order above. The important part here is to only use 1 Barracks, as maps with narrow land access often have 1 side with containers towards the enemy, while the other side is completely protected from them (especially in 2v2), so there is no rush to collect them too quickly.
The resources saved in that way are instead used to get the maximum amount of Supply Centers possible and start upgrading the Headquarters to level 2 as soon as possible, to get a strong start into the early naval combat and gather as many containers as possible there.
At this point it is very important to scout the enemy shipyard in some way, as going for 2 Shipyards through upgrading to HQ3 can leave one's base open to a lvl 2 naval unit rush. If spotted in time, it is recommended to add the planned in naval platform earlier than normal as it will buy enough time to get out Vikings and defend with those instead.
From this point on Viking production should be the main priority, so as to try and overwhelm the enemy navy with sheer numbers. This works especially well when the enemy mainly focuses on Alligators and not too many Naval Platforms nor avia.
If the enemy goes for Dragonflies, it is possible to add a 3rd Shipyard and then start adding Deltas which can deal with them without any issues as long as there are sufficient numbers as they are both cheaper and have better CP efficiency. This also works against the soon to be released Wasp. The same unit can also be used to reach enemy buildings outside the range of the Vikings as it has the ability to cross from the water onto the land as long as there is a beach connecting them.
If the enemy adds a lot of Naval Platforms it is recommended to get a lvl 3 Shipyard and start adding Poseidon as they have a high ranged ground attack that can out-range Naval Platforms and either destroy them without losses, or force the enemy into an offensive with their Alligators. The same unit is also the best addition to the Viking army when defending against Hawks.