See subject. Barring the primeval 2001 sock-'em with a bone moment,
So far, off the top of my head:
Hannibal, elephants
Hannibal, snakes on a boat (shout out to Tamerlane in current thread on viable combat animals!)
Hiroshima A-bomb
Israel '73 (I think), Syria, UAVs
Kuwait, Saudi, Israel, 1991, Patriot ABM
Israel 2012, that tank anti-tank missile thing ( help?)
Battle of Agincourt, the English Longbow. To be fair, it also included the use of knee-deep mud and heavy French armor.
I wasn’t able to find the specific battle, but I remember reading that the introduction of the first successful two-handed sword resulted in a great many bodies missing both legs at the knee.
To continue the trend (towards inferior armor rather than superior weaponry…), the Battle of Wisby resulted in a great many dead due to the defenders not having advanced their armor past the point of riveted mail & leather leggings, while the attackers were heard to say something on the order of “ooh, hey, shiny axes…” again resulting in a great many people losing limbs, with the number of dead rising so high that they couldn’t be looted in time (in the height of the summer), so they were buried en mass still in their armor.
All the Israel ones are wrong. UAVs, ABM and Active tank protection measures were in use long before the OP believes. UAVs were extensively used in Vietnam and as far back as WW2. The US and Soviets both deployed ABMs before the 1972 treaty took effect. The Soviet Naval Infantry had active protection measures on their tanks from the 1970’s and they saw extensive use in Afghanistan.
Come to think of it, Hannibal elephants is wrong as well. It was used in the Sub Continent for thousands of years before Hannibal and by Hellenistic rulers in the East.
Perhaps the September 7, 1776 attack of the submarine Turtle on the HMS Eagle in the New York harbor. This was the first submarine attack though it was completely unsuccessful.
The Gatling Gun was first used in war during the U.S. Civil War on the Union side, but I don’t know which battle. It wasn’t an official weapon of the Union Army however.
The Battle of Leyte Gulf, 1944, first organized use of Kamikazes (though I don’t think that’s what the battle is most remember for nor did that weapon have much effect on the outcome.)