Video game submarine combat has traditionally been represented in slow simulators with scary and serious names: Silent Hunter, Dangerous Waters, Hunter Killer. Nintendo's Steel Diver: Sub Wars, recently released on the 3DS e-shop, is a slightly incongruous addition to the genre. Where other sub-centric games have only the cold ocean and computer-controlled cargo-carrying targets for company, Steel Diver: Sub Wars fills its watery arenas with speed-boost gates and spinning boxes that magically repair damage. One such arena takes place in a swimming pool, complete with floats to mark out lanes. Check the menus, and you'll find anthropomorphic rabbit Peppy, on loan from Nintendo's Starfox series.

Steel Diver: Sub Wars is also strange for its payment model. It's the first of Nintendo's free-to-play games to reach the US — the other, Darumeshi Sports Store, will be released as Rusty's Real Deal Baseball in April — and it offers its base game for free. Anyone can play two single-player missions and compete in online and local multiplayer, but those who pay $10 can get access to new single-player missions and a host of new playable subs. It's a model often found in smartphone gaming, a market Nintendo has said it will enter in some capacity soon.

Even with its cheery, cheesy additions — players can only chat by inputting Morse code dots and dashes — Steel Diver: Sub Wars is a surprisingly tactical game. Teams of submarines, four to each side, have to maneuver carefully to avoid being flanked, with player-captains having to anticipate attacks on a three-dimensional plane. Enemies, if they spot you, will invariably start loosing their complement of torpedoes. Those torpedoes come in two varieties: standard models, which fire in a straight line; and homing varieties, which require a sub's captain to hover their crosshair over the offending enemy to secure a lock-on. Both types are achingly slow in their travels, making anticipation key when choosing to fire at a far-off foe.

Movement is similarly ponderous. Different submarines vary greatly in their strengths — some carry more torpedoes, others boast stronger armor — but none but the very quickest will be dodging accurately fired close-range torpedo volleys. Careful Steel Diver: Sub Wars players will hang back from a battle and watch from below, choosing paths of attack that present their enemy's broadsides. The most cautious will make liberal use of the "masking" option. When activated, this ability covers your craft in apparently magic bubbles that render it invisible for a short period of time. But that invisibility doesn't also gift invulnerability — torpedoes on collision course will still smack into your steel hull, even if you can't be seen.

Steel Diver: Sub Wars' pace rewards a measured approach, but it can also frustrate. There's almost no escaping a four-sub wolf-pack if they spot you on sonar, and a bad angle of attack can sink you before you're a minute into a match that runs for another five minutes. Some of the maps, too, aren't ideal for repeat sessions, with featureless open water offering little in the way of tactical options or space for a daring escape. In comparison with other strategic, slow-paced free-to-play success stories such as Wargaming's World of Tanks, Steel Diver: Sub Wars doesn't have the variety of terrain to make every match memorable.

Paid-for submarines don't feel overpowered in comparison with their free peers: with the right plan, a player with a free level-one craft can quickly and easily ruin a premium sub. Fighting players in the most advanced machines can be a harrowing experience, but it's hard to tell if the fear comes from their sub, or the imposingly large number next to their name, signifying dozens of hours of playtime.

The $10 price is a markedly low one in comparison with free-to-play peers that'll let you clear out your wallet for their multitude of microtransactions. This is Nintendo's first real try at free-to-play, and you can feel it testing the water with Steel Diver's submarines. Thanks to a pervasive sense of fairness in its in-game economy and the backing of solid, strategic shooting, Steel Diver: Sub Wars avoids any accusations of shading from free-to-play to pay-to-win, and sets the stage for Nintendo's future free-to-play efforts.