A Synchronous Multilayer Bomb (多層同期爆弾 Tasō Dōki Bakudan?, Yen Press: Multi-synchronous bomb) is a type of tactical weapon created in Academy City. It was part of BLOCK's conspiracy to assassinate Aleister Crowley.
It is a large bomb that has a number of high power explosives arranged in a regulated manner. A normal tactical weapon spreads an enormous blast over a large area while the synchronous multilayer bomb was made to focus a highly destructive blast on one small target so as to utterly destroy it. It was created in order to bomb an enemy stronghold in an urban environment with no civilian sacrifices.
Toaru Kagaku no Railgun
Toaru Kagaku no Railgun SS: Liberal Arts City
- Main article: Toaru Kagaku no Railgun SS: Liberal Arts City
Synchronous multilayer bombs were among the bombs loaded into the HsB-02s which were on standby during the attack on the Liberal Arts City by the Return of the Winged One while Academy City students were on a trip there, intended by the higher-ups to destroy the island and only recover Level 5 Misaka Mikoto, should the need arise.
Toaru Majutsu no Index
Battle Royale Arc
- Main article: Battle Royale Arc
BLOCK wanted to set off one of these bombs inside the Windowless Building in an attempt to kill Aleister Crowley. They planned this in an attempt to stop the chaos in the world from turning into a war. As the Windowless Building was impervious to even a nuclear attack they wanted to discover the route through which materials are brought into the windowless building. To do this they attacked the Reformatory in an attempt to take the Move Point's companions hostage and use them as leverage to find her identity. Once this was done they planned to negotiate with her to find the route they needed. In the end, however, GROUP was able to defeat BLOCK and stop their plans.