no one witnessed their heroism
Taken from Dan Abnett's Sabbat Martyr in the "Gaunt's Ghosts" series:
"Gaunt?" Biagi yelled from the walkway above. "Now?"
Gaunt paused and consulted his data-slate. They were all inside Old Hive now, all the surviving Regiment Civitas, the PDF and life company. All that could be expected anyway.
On his own list, the Tanith list, one unit was missing. Sergeant Skerral's number nineteen, last seen in a firefight with the death brigades on Neshion Street.
"Sir?" Corbec gazed at Gaunt. "I think we have to draw the line now."
Gaunt nodded.
"Seal the gates!" Biagi yelled. Leger placed his hand on the gene-reader plate and declared his authority. The massive blast shutters of the Old Hive gates clanged into place.
Nineteenth platoon were about five hundred metres from Old Hive's north entrance when they saw the gates close.
Skerral stopped in his tracks, and pulled the men up. Half his unit were dead. He ejected a cell from his lasrifle and slammed in a new one.
"Come on," he said, turning back to face down the slope at the waves of assault sweeping in. "Let's see how many we can kill."
The remnants of nineteenth lasted seventeen minutes from the times the gates closed. They accounted for one hundred and eight-nine enemy casualties. No one witnessed their heroism.
And more from 40k:
"We have explosives, sir." said Soric, saluting again for a good measure. " Mining charges we lifted from the store behind the smelteries."
"Static charges with no launchers... against tanks?"
"It's how we've been doing so far, sir: a man takes a warp of charges and runs with it, anchors it to the tank hull— "
"Suicide!"
Soric frowned. "Duty, sir. What other way is there?"''