O'Brian has been in 235 engagements in 22 years in Starfleet by season 4 of DS9, i.e., roughly one battle every five weeks. He's also served on a half dozen ships, including the Rutledge, Defiant, and Enterprise. This is an extraordinary total number of engagements, and a high frequency for such a great length of time. For an enlisted career naval officer with a family, leave time, and some length of service posted on stations rather than ships, this suggests that the past 22 years - as peaceful as they have appeared on paper - have involved a great deal of warfare, particularly as we are familiar in some detail with the portion of his record on board the Enterprise and Defiant.
The fact that he has been involved with 235 engagements with only six vessels suggests that Starfleet officers are very good at surviving battles with their vessels intact.
The Defiant's tractor beam can pick up a Jem'Hadar warship up out of the rock.
The scan cycle of a Constitution class vessel leaves up to a 3 second gap, but not very often (at least 3 minutes apart). A scanning field of more than 20 milliwatts from a tricorder will set off internal alarms aboard a CCS.
A graviton emitter can be made to fit inside a ring... suitable for manipulating the Dabo table. Dataport: Direct head-computer link.
A sensor array used by the Dominion detects cloaked ships at a range of 2 light years.
Weekly casualty list: 1730 names after "The Seige of AR-558."
Two middle-aged Ferengi can carry a Klingon cloaking device... which may be cloaked.
An Order represents 500,000 ground troops in the Cardassian military machine.