Great Britain's Olympic swimmers won two superb silver medals through Siobhan-Marie O'Connor in the 200m individual medley and the men's team in the 4x200m freestyle relay.O'Connor, 20, finished 0.3 seconds behind Hungarian world champion Katinka Hosszu, who set an Olympic record.
GB's men's relay team of Stephen Milne, Duncan Scott, Dan Wallace and James Guy were second to a dominant USA.
It takes Britain's medal tally at the Rio Games to six.
Four of those medals have come in the pool, after Adam Peaty's 100m breaststroke gold and Jazz Carlin's 400m freestyle silver.
O'Connor, from Somerset, swam a British record two minutes 06.88 seconds and nearly caused a huge surprise as she closed in on Hosszu, who has now won three gold medals in Rio and has dominated the medley for the past two World Championships.
But silver remains an incredible achievement for O'Connor, who suffers from ulcerative colitis [chronic bowel disease], as she became the first British woman to win an Olympic medal in the 200m medley.
"I was really confident coming into it because sometimes I can have disruptions. I felt in a really good place," said O'Connor, who finished almost two seconds ahead of the USA's Madeline Dirado in third.
"It feels pretty unreal. I am trying not to cry but it is the best feeling in the world.
"It doesn't seem real but seeing my family, I was getting choked up. It means everything. It has been tough but it is so, so worth it.
"Sometimes you think 'is it my time?' It just shows what determination can do and all the hard work has paid off, but I would not have been able to do it without my amazing team."
GB men launch late comebackBritain's relay team had come to Rio as world champions, but were not expected to challenge a USA team that included Michael Phelps, who now has 21 Olympic gold medals.
And even a silver medal looked unlikely for the British quartet in the early stages of the final, before Wallace's penultimate leg brought them past Australia to move into the medal positions and Guy overhauled Japan's Takeshi Matsuda on the final leg to secure second by 0.37secs.
Guy, who has missed out on medals in the 200m and 400m freestyle events, said: "The first few days were tough for me.
"I've got faster and faster the more I've been racing. The team is young and we'll be ready for the title at Tokyo 2020."
Milne added: "I can't believe it. These guys were amazing and it was a real honour to swim with them."
Who is Siobhan-Marie O'Connor?Born and raised in Somerset, O'Connor made her mark on the international stage aged 15 in 2011, winning 200m individual medley gold at the ASA National Championships.
She missed her school prom to attend the the 2012 British National Championships, where she won 100m breaststroke gold and booked her place as the youngest swimmer on the London 2012 Olympic team.
She failed to make it through her heat, but gained the experience of swimming in the medley relay final in front of 17,500 people.
O'Connor went on to win six medals at the 2014 Commonwealth Games, including 200 medley gold, before taking bronze in the same event a year later at the World Championships.
In July this year, she displayed her all-round ability by breaking the British 100m breaststroke record.
AnalysisDouble Olympic gold-medal winner Rebecca Adlington: "I think this is the best we have done for a very long time and we still have some big races to come.
"I am thrilled for James Guy, especially because this is extra special after the week he has had."
Former freestyle world champion Mark Foster: "As a country we have improved so much. We have strength in depth and there's character in the team. The future is bright."
BBC Sport chief sports writer Tom Fordyce: "A second special night in the pool for Britain's swimmers. After Adam Peaty and Jazz Carlin two nights ago, this was another story of personal bests produced when it mattered most, of the best possible result being taken on the biggest stage of all.
"No-one was going to catch Katinka Hosszu, just as no-one was going to catch a US men's relay team featuring Ryan Lochte and Phelps; in taking silvers behind both, O'Connor and the quartet of Milne, Scott, Wallace and Guy have put British swimming wonderfully back on course."