What does " that martinet's error " mean?
The officer," he reasoned, "will not make that martinet's error a second time. It is as easy to dodge a volley as a single shot. He has probably already given the command to fire at will. God help me, I cannot dodge them all!"

An appalling plash within two yards of him was followed by a loud, rushing sound, diminuendo, which seemed to travel back through the air to the fort and died in an explosion which stirred the very river to its deeps!

What does " that martinet's error " mean? Please..

Question

What does " that martinet's error " mean?
The officer," he reasoned, "will not make that martinet's error a second time. It is as easy to dodge a volley as a single shot. He has probably already given the command to fire at will. God help me, I cannot dodge them all!"

An appalling plash within two yards of him was followed by a loud, rushing sound, diminuendo, which seemed to travel back through the air to the fort and died in an explosion which stirred the very river to its deeps!

What does " that martinet's error " mean? Please..

Answer

The error made by 'that martinet'.
A martinet is a cruel, very strict military officer who cares nothing for the lives of his men.  The name comes from a famously cruel officer named Martinet, who had strict punishments for even the slightest mistake.
"I will commit the same error that he (the martinet) made a second time."