Kirsty Noble, 23, has been involved in the RNLI in Aberdeen for two years, and thought she was taking part in a routine training drill with colleagues.
The lifeboat captain picked her to take the lead in the exercise on Aberdeen's Fishmarket Quay, and Kirsty knelt down to tend to the 'casualty'.
But she was shocked to see her boyfriend, Sam Main, who was dressed in an RNLI yellow uniform and safety helmet.
Kirsty was so surprised she started crying, and Sam popped the question in front of her delighted crewmates, who had all been in on the plan.
The couple have been together for four years and first met in 2014 whilst working as swimming pool lifeguards at a local leisure centre.
Kirsty, from Aberdeen, said: "It was just amazing.
"I think he was nervous at first because he spent months planning it.
"He went to my captain and they came up with different scenarios and that was the best one.
"When I went down for training, my team captain said I would take the lead.
"It took me a minute to realise it was him.
"I just started crying because the penny had dropped.
"The moment went by so fast, it was so special - surprised is an understatement.
"It was an amazing occasion and to spend it with my best friends was very special.
"My friends all said they are coming to my hen party even though they are all guys".
Kirsty, a website designer by profession, is two years into her training and is a regular volunteer crew-member on both Aberdeen's all-weather and inshore lifeboats.
Sam, who works as an active school coordinator, had called the RNLI's Aberdeen branch to help with his elaborate idea.
He said: "It was an amazing day and I'm delighted that she said yes.
"A lot of planning went into the day so I'm so happy that it all went to plan.
"I'm really grateful to the whole RNLI team for all their help in making it possible."
Aberdeen Lifeboat coxswain Davie Orr said: Aberdeen's volunteer lifeboat crew is a very close-knit team - we go through the highs and lows of search and rescue missions together.
"This was a special opportunity to share in the happiness of one of our own.
"We all wish Kirsty and Sam every happiness."