Science fiction novel with the title "T" (which is also the name of the protagonist)

Question

I'm pretty sure the title was "T". It's about an alien race at war with humans. They decide to end the human race by destroying Earth before humans evolve. They send some humans through space and back in time to do the job.

I think the humans have single letter names (A, B, C, etc) They have raised/cloned the humans just for the job and to save space in their ships they have only a head, a body and one arm. Most don't make it.

The aliens don't know that there were 2 more planets in the past and they count the planets in from Pluto. One human hits a planet and completely destroys it and T hits a glancing blow and just breaks up his target forming the asteroid belt.

Answer 1

This is Brian Aldiss's "T" from 1956.

Amazon Review:

`T' (1956) (7 pages) 3.75/5 (Good): In the distant future a strange alien mutant with one arm is breed to navigate an interstellar missile. Pumped with nutrients and subjected to periodic propaganda, it steers its deadly bulk towards Earth. The story is weakened by a silly -- but funny -- time travel ending. The visceral image of a mutated one-armed barely sentient alien on a suicide mission that takes thousands of years to reach its target all the while listening to the same propaganda message over and over is an incredibly disturbing vision...

I found it by doing an ISFDB search for stories with a title of exactly "T" and then started searches by a combination of that title, the author's name, and publication date. That brought up the Amazon page when I looked for Brian Aldiss "T" 1956 and I looked to see if the reviews had more details, which one did. Seeing the "one arm" bit clinched it for me.