Vanoraxian Polar Expeditionary Marines

The Vanoraxian Polar Expeditionary Marines are a specialized tip-of-the-spear unit made up entirely of white dragons and white dragonborn. They are an elite unit that is particularly effective in an archipelago. Why? Water and cold. They specialize in the use of ice.
White dragons hail from the coldest regions of the world and for much of their lives, they are more like an extremely intelligent apex predator, really only reaching typical levels of draconic intelligence as they mature. White dragonborn, however, are as smart as humans or elves from the jump, and dragon and dragonborn alike are extremely adept at the use of ice magic for far more than just attacking enemies on the battlefield.
Ice, as it turns out, makes excellent ships and fortifications, and so these troops sail what are essentially small icebergs to where they want to attack (especially resistant to being sunk because the entire ship is bouyant) and then establish a beachhead and quickly fortify with with forts made out of more ice.
This has several key advantages: the ice makes excellent fortifications both in terms of durability and ease of repair; as long as there is water nearby, it's easy to repair damaged sections of wall. Local material is often mixed in, and a common tactic is to essentially make a stone wall with ice as the mortar and then glaze it with additional layers of ice. The sigils used to maintain the ice magic can also be fine-tuned to allow exterior surfaces to melt slowly making them extremely slick with a layer of water. If a position is overrun, the magic can quickly be canceled, melting the fortifications almost instantly and denying them to the enemy.
Ice mages in the ranks often travel with other troops once the force is inland, and can quickly make small ad-hoc fortifications in response to tactical situations that arise.

Type

Marines