By Ian Pannell
BBC News, HMS Cornwall in the Gulf
The thing about extraordinary days is how they invariably start out in a routine fashion. Friday on board HMS Cornwall was one of those days.
HMS Cornwall is operating in the northern Gulf
The Royal Navy and the Royal Marines, together with American, Australian and Iraqi support, patrol some of the most important waterways in the world. Their mission is to protect the oil terminals that effectively keep Iraq's economy afloat.
Precise figures are rare but oil exports account for as much as 90% of Iraq's GDP.
Just the day before, we watched the sailors and marines stop and search suspicious-looking boats, and we talked to them about the lives and families they had left behind in Britain.
One young sailor told me about the guilt of leaving home and the agony of trying to be a good parent and a good sailor.
They talked about lifelong ambitions to go to sea. There was agreement that, although the work was hard, morale was high.
Many of the team we spoke to that day would be captured at gunpoint less than 24 hours later.
Friday began the same way as the day before. The helicopter took off and the two black inflatable boats and their crew were put to sea, on the same routine patrols we had seen.
We were on the deck of the Cornwall with the crew on hand with logistical support, cups of tea and large doses of banter. Then everything changed.
The path was suddenly barred by a junior officer who held up his hand and asked me to wait outside
I stepped onto the bridge of the Cornwall, but the path was suddenly barred by a junior officer who held up his hand and asked me to wait outside.
No-one wanted to talk or make eye contact. Our ever-cheerful minder was hauled off while we stood in a corridor waiting, trying to deconstruct what was happening.
We were called in to talk to Commodore Nick Lambert, the coalition task force commander. A genial host, he had already given us the kind of welcome and insight that is rare among the often starched diffidence of military men.
But now he was tense.
"We have lost 15 people," he said.
He explained how the 15 sailors and marines had been surrounded and captured at gunpoint. They were already being held at a small Iranian naval base across the border.
For the moment, we were sworn to secrecy while the Ministry of Defence and the Foreign Office were alerted and the families contacted.
The personnel would have been in boats similar to those pictured
Then the ship's public address system crackled into life and the voice of Cdr Jeremy Woods brought HMS Cornwall to a standstill.
For a few brief minutes, the seemingly incessant noise of the Cornwall stopped. The decks, the mess hall, the engine room and galleys of the naval frigate were silent.
Hardened sailors hung their heads, pensively listening to how 15 of their friends and workmates had just been captured.
Cdr Woods gave them a sombre but positive assessment.
"Our crew have not been harmed and have been taken to a place of safety," he said.
He warned this would have a significant political impact and high-level discussions to secure their release were already under way.
"We are doing our best to get our people back."
He promised that the crew would not run off and desert their colleagues.
"Let's get the job done," he added.
HMS Cornwall and its crew have seen hard times before.
Through its many incarnations it has known war and peace.
But this week will be remembered as one of those hard times.
When we had first arrived on board, Cmdr Lambert had taken us to one side to tell us how critical his mission was.
He said it was derisively called "the wet end" or "the safe end" of Iraq, an expression guaranteed to annoy the hell out of everyone serving these waters.
They won't call it that any more.
There are hard days ahead aboard HMS Cornwall but, to a man and woman, the crew remain upbeat and confident their colleagues will be home safe and soon.