This was an attempt to make an effective crowd-control Wave Cannon. Upon impact with an enemy or obstacle, the bolt breaks into two smaller bolts that rebound slightly, then continue forward, shrinking in both size and power with each impact. The size of the bolts depends on the charge level released; after several impacts, a bolt will no longer have the sufficient power to split again and will simply end.
Description
From R's Museum:
2 Loop Max. After hitting an enemy or some other obstacle, the beam splits and increases the destructive potential of the gun.
Appearances
R-Type Final
Normally found on the R-9WB Happy Days, but also part of the Hybrid Wave Cannon System 3 on the TL-1B Asklepios.

R-Type Final 2
The beam splits are more focused, making it extremely effective on a single target, namely a boss. For example, a 2 Loop charge can one shot the core of the Distraction warship boss even on R-TYPER 3 difficulty.
Besides the R-9WB Happy Days and the Hybrid Wave Cannon System 3 on the TL-1B Asklepios, the Split Wave Cannon is also found on the Huge Bydo Fenrir, which presumably imprisoned the Happy Days as its head.
R-Type Tactics II: Operation Bitter Chocolate
Equipped by the R-9WB Happy Days.