On watercrafts I was on board. What am I?
From ODO: 3.1 An apparatus capable of both receiving and transmitting radio messages between individuals, ships, planes, etc.
Boats/ships used (still use) radios for communication.
A part of me's mechanical.
Tuner/switches were traditionally mechanical.
The other is electrical.
Otherwise it primarily works with electricity.
I'm named after an ancient word.
Latin origin. From etymonline:
"wireless transmission of voice signals with radio waves," 1907, abstracted from earlier combinations such as radio-receiver (1903), radiophone (1881), radio-telegraphy (1898), from radio- as a combining form of Latin radius "beam." Use for "radio receiver" is first attested 1913; sense of "sound broadcasting as a medium" is from 1913.
On watercrafts I was on board.
Same as title.
My weaknesses helped to kill some men.
As a prefix, my activity (radioactivity) resulting from instability (synonymous with weakness) of an atomic nucleus resulted in creation of the atomic bomb and consequent loss of lives.
Thus I am remembered now and then.
Perhaps a reference to remembrance like during anniversary of Hiroshima/Nagasaki bombings.
My weakness not only demanded some blood.
It changed history to the good.
The devastation and loss of lives due those bombings meant the whole world woke up and it is very unlikely that such destruction will happen again.
All in all I am quite small.
I'm about six inches tall.
Typically portable radios (apparatus capable of both receiving and transmitting radio messages) are around six inches tall.
I contain a battery.
Which spends the electricity.