Along with swimming smooth, swimming with sustainability, or swimming endurance, is the most important skill for a triathlete to have. It does a triathlete no good to get out in front of the pack, swim strong to the first buoy, then completely come apart and struggle the rest of the way. The ability to sustain a high intensity is paramount, behind only smooth in importance. Having a pretty stroke for half the race and then watching your arms come off and float to the bottom of the ocean isn’t terribly useful.
More: 4 Steps to a Smooth 1.5K Swim
As stated, a major part of sustainable work will be focused on maintaining smooth swimming. The other focus of sustainable swimming is being fit enough to allow you to get out of the water after 1.5K and blast up the beach, through T1 and out onto your bike.
These will be longer sets, much like your long, slow-distance runs and rides. Maintaining a steady pace and heart rate is the goal, not cranking it to 11.
Be sure to warm up before you go into your main sets with 200 to 500 yards nice and easy. This should shake the cobwebs out and get the blood into your muscles. You can also use active rest, 50 to 100 yards easy.
Please note that under set #2 there are many ideas for drill variation. Be creative with this. These are guidelines and ideas. They can be used on almost any of these sets. Many of the other sets also have variation possibilities.