I am often surprised at how small some people think the USS Enterprise-D is, when compared to other ships in the fleet. The truth is, it’s not small at all. In fact, the Enterprise is one of the largest starships ever constructed by Starfleet -- or any Federation member planet.
The Enterprise, like the other five Galaxy-class starships in service, is 2,108 feet (642.5 meters) long, and 641 feet (195.3 meters) tall. It can comfortably house up to 2,526 personnel, and it has enough amenities to qualify as a small city. Starfleet is even deploying Galaxy saucers, by themselves, as functioning deep space starbases, three of which are already in service.
To date, the Romulans are the only species known to have built starships larger than the Enterprise, and even then, we don’t know everything about their technical capabilities.
-Lieutenant Sam Archer
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August 3, 2364 -- (Original Devron Timeline)