The SS Beagle was a 23rd century Federation class 4 survey vessel operated by the Merchant Service. The Beagle had a crew of forty-seven and was commanded by Captain R.M. Merik; his flight officer was William B. Harrison.
The Beagle was the first ship to survey the star sector where the System 892 was located when it disappeared in 2262. During its mission, the Beagle suffered meteor damage and Captain Merik went ashore to the star's fourth planet to obtain iridium ore for repairs.
While on the planet, they were met by the local inhabitants, led by Proconsul Claudius Marcus. The Proconsul believed it would be unfair, even ruinous, to his highly conservative society if word of its existence should be carried elsewhere. Merik, convinced that this fine world should not be contaminated, had the remainder of his crew beam down and the Beagle was left to be deserted. . Some of the crew took to their new home and became citizens, but the others, who refused to adopt the ways of this society, were thrown in prison. Regarded as captured barbarians, they were forced to fight as gladiators.
Abandoned, the wreck of the Beagle drifted for six years before it was found, approximately 1/16th of a parsec away from 892-IV, leaving behind in its debris field portions of its antimatter nacelles and the personal effects – but not the bodies – of the crew.
Following the discovery of the Beagle's debris, the USS Enterprise visited 892-IV to determine their fates. Merik, for one, had done very well for himself, having secured a high place in imperial politics. As for his crew, Merik told the Starfleet landing party that "those who were able to adapt are still alive". Kirk and Spock, however, witnessing the death of Harrison on Roman television, had heard him sports-commentated as "the last of the barbarians". Kirk did not press him on this issue.
Merik would have been removed from the planet to face charges of violating the Prime Directive had he not died saving the Enterprise landing party from Marcus and his machine gun-toting police. (TOS: "Bread and Circuses")
According to John Kneubuhl's 10 May 1967 draft of the script, this vessel was originally known as the "USS Intrepid". This name was struck by de Forest Research, noting, "The name Intrepid has been used before in 'Court Martial' with no implication that she had been lost. A suitable name for star ship [sic], suggest: 'Resolute'." In the same draft, the registry was given as "37-SC1"; de Forest noted, "This number does not conform to precedents established in Star Trek," and "suggest: change number to NCC-1698."
Following a rewrite by Kneubuhl and Gene Coon (dated 7 September 1967), the name "Intrepid" was dumped in favor of the name "USS Lord Nelson". De Forest once again rebuffed the name, noting, "Star Fleet [sic] nomenclature has indicated that star ships [sic] are named for abstract qualities, e.g. Enterprise, Intrepid, etc. Suggest as per original notes 'Resolute'. Personal names are used for shuttlecraft, e.g. Galileo in 'The Galileo Seven'."
The final rewrite by Coon and Gene Roddenberry (dated 15 September 1967) replaced the name "Lord Nelson" in favor of the name "SS Beagle". While not named the "Resolute", as per de Forest's insistence, he was seemingly satisfied with the name change, stating, "No conflicts for non-government ship."
The wreckage noted in dialogue from the Beagle was added to be seen briefly onscreen in the remastered airing of the episode, consisting of miscellaneous shapes of the outer hull.