It is possible to get a Level 1 Rear Weapon in both the Super Arcade Mode and Super Tyrian. To get this, you have to gain access to the Saw Blades secret level in Episode 3 and destroy ALL Carrot ships and get the Hot Dog icon.
Consequences: Your front weapon changes into the Hot Dog Front with the corresponding level according to the amount of lives you have and you gain a Level 1 Hot Dog Rear (the two hot dogs which fire in a up-left and up-right in turns) which remains permanently yours.
In Super Arcade, you can still switch to the front weapons your current ship has available (like Mega Pulse, Lightning Cannon, Rear Mega Pulse, Sonic Impulse and Protron Wave for the StormWind), but you will not regain the Atomic Railgun in Super Tyrian; you will permanently have the Hot Dog Front.
But still, I believe you have more fire power since you do have eight hot dogs at Level 11 Hot Dog Front.
Also, the Tab + # still work in Super Arcade, so you can have both the Level 1 Rear Gun AS WELL as the Sidekicks assigned to that specific number to generate/change your ship.
Also, when using the Tab + # mark in the Super Arcade in Tyrian 2000, your Repulsor becomes a Super Repulsor; keep whatever button you use for the Special Weapons pressed during the level, and most, if not all enemy bullets won't even come NEAR you!