This Gamemode would be like battlefield 1's operations mode, it would consist of 3 different rounds
I will be using red team and blue team as examples. THe round would start if red team doing a naval assault to a fort controlled by the blue team. Blue team will have a limit on the amount of respawns while red will have unlimited if the blue team holds the fort (by not allowing the red team to capture the capture point in the fort) then they win. However if they are unable the red team will take the point and move to the next round. However the objective could be a rush style objective like planting dynamite at the gate (that blue team can diffuse) and if the gate explodes red team wins, that is another way u could do the first round so first and second don't have same objective
The second round would be a land battle in the fort, this would be mainly close quarters combat (what would be quite unique) and would have red team trying to push blue team outside of the fort. Red team would have to push and take the capture point at the land entrance of the fort. If red team does then it will move to a third round (or only have these 2 rounds)
As stated above this round isn't completely needed and could just end on the second round, however in the third round the blue team would carry out a counter attack on the red team who just took the fort. Red team will now have a limit and would have to stop the blue team from taking the middle of the fort if blue team succeeds then they win if not red wins.
Conclusion and extra thoughts
I think this gamemode would be great for casual play and i would expect this mode to come in later after the full core game has been realised (just like my proposition on commander battle) This gamemode would incorporate the 2 main aspects of the game fully (naval and land warfare) and every class would have a role including sappers etc (although they are not confirmed). Each map for this gamemode could also play differently or example one map the game could end with a straight up naval to naval combat to stop blue team from evacuating and retreating. The Nations ofc can also be switched so u could have England attacking france defending and vise versa
Be aware the gamemode does need some fine tuning and that is where i wish for the community to give feedback on the gamemode to make it the best it can be, also if the map is based on a colony then the third mode would be a retreat from the defending force once the fort is taken. However if its in mainland then the 3rd round would be as shown above and the fort garrison would be reinforced and there would be a counter attack
I hope you take this into consideration and i wish for anyone who reads this to leave their opinion and ideas that could further make this potential gamemode better. I think of this gamemode as a evolution to both naval siege combined with normal line battles to make a massive battle perfect for casual play