Now this really is efficient (and fast) swimming! Watch Olympian Jono Van Hazel's near perfect stroke technique just before your next swim and reproduce his smooth movements when you jump in the water: a very powerful way to improve your swimming.
Notice that while Jono has a very long freestyle stroke technique he doesn't achieve this by gliding (a very common misconception amongst swimmers). Instead he has low drag and fantastic propulsive technique which gives him great distance per stroke.
Whilst he has a long stroke, he also has great stroke rhythm - the real secret to great swimming. Our 'time between strokes' measure shows that Jono has nearly zero gap between finishing one stroke and starting the next. (In fact when he's swimming quickly there's even a slight overlap between strokes.) His lead hand is constantly in motion, either extending forwards, catching the water or pressing it backwards: great catch technique and no over-gliding.