If I had to choose the missile that Arthur valued the most among all, it would definitely be the existing Dove-style missile, and specifically, the ship-borne version of the Dove-style missile.
Honestly, among the navy, army, and air force, the navy of Australasia is currently the weakest.
Although the army isn't large in scale, it is at the forefront of the world in tank technology and possesses extremely formidable firepower. In addition, with the allied support of Kalimantan and the Philippines—two vassal states—there's no need to worry about the army.
There's no need to say much about the air force. If the air force of Australasia dares to claim second place in the world, probably no other country would dare to claim to be the first. However, that presupposes that the air force capabilities of all countries are revealed, not hidden away like Australasia's.