Its not a DUR or the like. Best explanation is to be found within the Q&As part 2: https://robertsspaceindustries.com/comm-link//15478-Anvil-Terrapin-Q-A-Part-2
"(...)The Terrapin was designed first and foremost for the UEE Military to provide overwatch, long-endurance picket, and reconnaissance capabilities to the fleet, as well as extend the Navy’s ability to provide a patrol presence to border systems that couldn’t be allocated capital ships or large fighter garrisons for defense. These capabilities lend themselves to civilian use as an explorer, particularly where a private operator principally gathers and sells information, point of interest data, risky deep scans of hostile environments, and survey data for a living, as opposed to collecting tangibles for sale. The Terrapin’s long endurance, advanced sensor suite, and range play to this aspect of exploration, whereas other explorers like the Freelancer DUR sometimes focus more on collecting trinkets, incidental salvage, and other physical items to supplement their exploration runs. While purpose built for recon, overwatch, and picket duty, the military makes good use of whatever is available, so the Terrapin’s supplemental military roles as an S&R ship or makeshift troop transport arose as a matter of need, in situations where the tried-and-true Argo wasn’t sufficiently robust for service under fire.(...)"
"(...)The Terrapin was designed first and foremost for the UEE Military to provide overwatch, long-endurance picket, and reconnaissance capabilities to the fleet, as well as extend the Navy’s ability to provide a patrol presence to border systems that couldn’t be allocated capital ships or large fighter garrisons for defense. These capabilities lend themselves to civilian use as an explorer, particularly where a private operator principally gathers and sells information, point of interest data, risky deep scans of hostile environments, and survey data for a living, as opposed to collecting tangibles for sale. The Terrapin’s long endurance, advanced sensor suite, and range play to this aspect of exploration, whereas other explorers like the Freelancer DUR sometimes focus more on collecting trinkets, incidental salvage, and other physical items to supplement their exploration runs. While purpose built for recon, overwatch, and picket duty, the military makes good use of whatever is available, so the Terrapin’s supplemental military roles as an S&R ship or makeshift troop transport arose as a matter of need, in situations where the tried-and-true Argo wasn’t sufficiently robust for service under fire.(...)"
