The crew made a conscious decision not to engage the Iranian Revolutionary Guard personnel who took them captive, they said at a news conference at the Royal Marine Base Chivenor in England on Friday.
Later on Friday, Iran dismissed the news conference as a "staged move" and said that it could not cover up the mistake made by British military personnel.
The sailors and marines were released in Tehran on Thursday after a tense standoff with Iran.
Several members of the group were displayed on Iranian television and made apologies for apparently having entered Iranian waters.
British ministers said the so-called confessions appeared coerced.
Inside Iraqi waters
"Fighting back was simply not an option," Royal Marine Captain Chris Air said at Friday's news conference.
"I can clearly state we were 1.7 nautical miles from Iranian territorial waters."
The navy personnel could do nothing to avoid capture, he said.
The men also said Leading Seaman Faye Turney, 26, the sole female crew member, was isolated in a cell away from the rest of the crew.
Iran used her as a "propaganda tool", keeping her isolated and telling her she was the only one being held, the group said.
They said they were "incredibly proud" of Turney and the "highly professional" way she conducted herself throughout the detention.
"The fact that she's a woman has been used as a propaganda tool by Iran. This is deeply regrettable," they said.
Taken to prison
After their arrest in the Gulf on March 23, the sailors and marines were taken to a prison in Tehran.
"We were blindfolded, our hands were bound, we were forced up against a wall," the statement said.
"We were interrogated most nights and given two options. If we admitted that we had strayed, we would be back on a plane to the UK pretty soon. If we didn't, we faced up to seven years in prison."
Reacting to the British soldiers' comments at Friday's news conference, Iran said it was "staged" to cover up the British soldiers' illegal entry into the Islamic state's territory.
"The propaganda and the staged show cannot cover up the British military's violation of the Islamic Republic of Iran sea border and their repeated illegal entry," Mohammad Ali Hosseini, a foreign ministry spokesman, said.
A separate Iranian foreign ministry statement said: "We are sorry that Britain has no knowledge about Islamic culture and Iranian civilisation to understand the reason Iran pardoned the British soldiers."
For its part, the White House on Friday condemned as "unfortunate and extremely disappointing" any mistreatment by Iran of British naval personnel.
"What the sailors said this morning is unfortunate and extremely disappointing if they were treated inappropriately in any way," Gordon Johndroe, national security spokesman, said.
"If what they described is accurate, and I have no reason to believe it is not, if what they described is accurate then that would not seem to be appropriate behavior and action."
Meanwhile, in a related development, Britain has suspended boarding operations in the Gulf and is reviewing rules of engagement in the area's waters after the incident, according to Jonathan Band, the UK navy chief.
He said British forces were reviewing how they are handled in future amid disquiet over how easily the sailors were seized on March 23.
"As part of this ongoing review, the operational procedures and the rules of engagement that go with them will be reconsidered," Band told BBC Radio on Friday.
Iran still holds the only two boats used to carry out the search operations in the area.
Güncelleme Tarihi: 20 Eylül 2018, 18:16