"Flying Shark" and "1943" redirect here; some magazine reviews mislabel this game as such, though Twin Hawk does bear a resemblance to the former. Aside from that, though Flying Shark was never ported to a Sega system, that game's sequel, Fire Shark, was.
Twin Hawk, originally released in Japan as Daisenpu (大旋風), is a 1989 arcade shoot-'em-up by Toaplan. It was ported to the Mega Drive by Sega in 1990, and released exclusively in Japan and Europe.
Like many of the Mega Drive Toaplan ports, a single cart with multiple regional versions was made for all releases of the game, and these can be switched between simply by playing the cart on a particular regional model or by using Game Genie and the like. Attempting to play the cart on an American Genesis triggers the slightly easier "Twin Hawk" version.
Twin Hawk is one of Toaplan's most straightforward games, unusual to see so late especially after the likes of Truxton. Despite this, Twin Hawk has a number of interesting traits that not many games do: there are absolutely no breaks and the entire game is essentially one giant level, and there are only land and sea enemies to be fought, among other things. The most major of these is the ability to call in a formation of six white "Helper" planes similar to your own, that shoot with you and even divebomb the nearest enemy when each is shot. Unfortunately, when used correctly, these can completely trivialize the game...
and shoot, and basic rapidfire is available in the options. summons the "Helper" planes; pressing pressing again before the formation completes (when they'll start shooting) will trade the Helpers for a typical "bomb" attack like other Toaplan titles, while pressing at any point after the formation is completed will force all remaining Helpers to divebomb.
There are three different types of powerups, released by destroying specific non-hostile trucks (land) and boats (sea), painted in various colors to show with powerup they release:
Green trucks and boats do not drop anything, though they give you points for destroying them. All trucks/boats start off as green and change color depending on certain conditions. For example, if you have no powerups (such as after dying), certain trucks/boats will be orange.
Orange trucks and boats release orange S icons, which upgrade your regular shot. This can be upgraded three times (four sets of two bullets), after which all scheduled orange trucks/boats will be green.
White trucks and boats release white H icons, which add another Helper to the Helper stock. They seemingly never appear when you have two Helpers stocked, and appear frequently when you have none.
Blue trucks and boats release blue plane icons, which add an extra life to the life stock. These are extremely rare, likely triggered with lower life stocks.
While Twin Hawk is more or less one giant stage with numerous boss-like enemies, the game is functionally divided into four large areas, punctuated by a change in music (and specifically marked in ports). There is a particularly large tank as the final boss, after which the game begins again at a higher difficulty, etc.