Tracing the history of the classic bomber attack...

[Skyknight]

So let's see...the precept, at least, dates to Defender (limited supply of weapons that instantly destroy every enemy onscreen). The way we know them, though (i.e. wide area effect, more heavily damaging that outright death), seems to have begun with Tiger-Heli.

What I'm curious about is, when did we start having the version that burned away enemy projectiles? (Defender doesn't count here.) Sky Shark seems a little too young for it to be the instant correct answer--Tiger-Heli was published in 1985, Sky Shark in 1987. I'm half-expecting to find an answer in 1986...

[trap15]

Tiger-Heli's bombs burn enemy bullets. I think it's probably the originator of the bomb concept.

[Skyknight]

...? Could have sworn that they didn't. Maybe I'm misconstruing the interview I saw which stated that Toaplan intended the TH bombs to be offensive weapons, rather than defensive. Perhaps you're thinking of how if an enemy bullet strikes the bomb sprite exactly, the bomb goes off rather than the player being shot down?

[trap15]

No, I'm quite sure it deletes bullets that it hits. They may be intended to be offensive, but they'd also be a bit useless if they didn't delete bullets.

[Mortificator]

The two key interviews are both courtesy of blackoak: this one with Yuge and this one with Uemura.

Xevious has bombs that impact a certain distance in front of the ship and are used offensively against ground targets. Yuge tells us that Xevious influenced the design of Tiger Heli, whose bombs he and Uemura say were also intended for offensive use. We can see from Tiger Heli that there are four key differences in its bombs when compared to Xevious:
* limited in number
* work on both ground and air enemies
* have a blast radius
* neutralize bullets within that radius

Both Yuge and Uemura noticed that players ended up valuing the defensive bullet-neutralizing aspect of bombs more than the offensive. I think Toaplan's library shows an awareness of that, as bombs (with some exceptions) grew in defensive value, culminating in the get-out-of-jail-free card of Batsugun Special. Ikeda carries that design element over to Cave, which cements it in the genre.

This line of development ended up producing bombs with similarities to the ones Defender had way back when, but I don't know that I'd say Defender was a direct inspiration.

[BareKnuckleRoo]

No, I'm quite sure it deletes bullets that it hits. They may be intended to be offensive, but they'd also be a bit useless if they didn't delete bullets.

Speaking of which, I can't think of many bombs that don't erase bullets. The few I can think of don't do so on purpose and are still very safe (Perfect Cherry Blossom, Sakuya B, you freeze bullets to graze for score). Or Strania, where your invincibility move isn't really a bomb per se, but a short duration shield.

[Mortificator]

^ That reminds me of another early invincibility move: the loop from 1942.

Also, it looks like some posts disappeared in the time between my clicking "post reply" and "submit."

[BareKnuckleRoo]

Formation Armed F featured the formation special attacks that appeared much like bomb items and boosted power and formation with temporarily without offering any invincibility or bullet clearing. In fact they were dangerous to use as you moved your shot-blocking pods away from your ship, making it much easier to get hit...

[Skyknight]

I can think of at least one bomber that doesn't neutralize bullets--the JAS-39's Grand Napalm in the first Aero Fighters, probably because its normal Float Mine weapon could already destroy projectiles. Granted the AJ-37's bomber didn't burn bullets either, but at least it gave you temporary invincibility.