Pressed repeatedly for a "specific response" by Sen. John McCain, Carter suggested that the U.S. initially was readying a rescue attempt.
"At the time of the incident, we prepared to protect our people," he said, but "it turns out they were released in time" before a rescue could be mounted.
Since then, the U.S. has "made very clear that that's the kind of behavior we wouldn't want" to see happen again, Carter said.
Earlier, in his prepared remarks for testimony to the Senate Armed Services Committee, Carter said that "given this Committee's particular interest in this, I want to say a few words about Iran's treatment of our sailors on Farsi Island back in January."
"As I've made clear, Iran's actions were outrageous, unprofessional, and inconsistent with international law -- and nothing we've learned since then about the circumstances of this incident changes that fact," Carter said.
McCain, an Arizona Republican and the committee's chairman, said that Iran was "exploiting the humiliation of American service members" and asked "what action you have recommended that we take in response to this?"
Carter said that the proposed defense budget was supporting thousands of U.S. troops and sailors in the region, as well as improvements to ballistic missile defenses.
McCain cut off Carter: "I wonder if you had planned on any specific action that the Iranians would know is the result of the humiliation of our service members. You've made it quite clear that you're outraged and all that."
Iran's official media has continued to trumpet the capture of the two boats, which had strayed into Iran's territorial waters off Farsi island in the Persian Gulf on Jan. 12, as a victory against U.S. aggression
On Tuesday, Gen. Ali Razmjou, a commander of the Iranian Revolutionary Guard, claimed that Iran had retrieved thousands of pages of information from GPS devices, phones and maps confiscated from the U.S. sailors.
At the time of the incident, the U.S. Navy said that two digital SIM cards in satellite phones appeared to be the only devices that were missing when the crews were released.
The two 50-foot Riverine Command Boats were on a routine mission to move from Kuwait to the headquarters of the Fifth Fleet in Bahrain when a near-farcical series of errors by the crews and their command sent them close to Farsi island, where they were boarded and seized.
The incident occurred as President Obama was preparing to make his State of the Union address and the U.S. was seeking to finalize the deal to rein in Iran's nuclear programs. The crews and the boats were released after about 16 hours following back-channel diplomacy by Secretary of State John Kerry.
The Navy has said that the boats went astray because of a "navigational error," but several reports by Foreign Policy and others, which have not been contested by the Navy, have detailed a series of problems that went beyond navigation.
One of the two boats had mechanical problems, and the crews had to cannibalize parts from a third boat, delaying their departure. The boats were off course and the crews failed to notice. Neither did the command in Bahrain, even when the boats failed to rendezvous with a refueling ship.
One of the two boats broke down, and both boats drifted into Iranian waters as the crews scrambled to make repairs. Small craft from the Iranian Revolutionary Guard then boarded and seized the U.S. boats and the crews at gunpoint.
The U.S. sailors were forced to kneel on deck. Iranians in uniform searched the boats and lined up confiscated automatic weapons and belts of ammunition.
Vice President Joe Biden denied that any apology was made to gain the release of the two boats and the crews, but the video from Iran's official Fars news agency showed a U.S. sailor saying, "It was a mistake. That was our fault, and we apologize for our mistake. We did not mean to go into Iranian territorial water."
"The Iranian behavior was fantastic while we were here. We thank you very much for your hospitality and your assistance," said the sailor.
-- Richard Sisk can be reached at firstname.lastname@example.org.