The combat swimmer stroke (CSS) is really the nick name for a modified version of the side stroke.  If you have ever seen military special ops (SEALs, EOD, SF, RECON, etc) swimming with fins on the surface, chances are it is some version of this underwater recovery stroke.  In a nutshell, it is a mix of the side stroke, breast stroke, and free style all rolled into one very efficient and fast swim stroke that enables special ops swimmers move in the water without splashes and a low profile.  Here is a three part breakdown video of the combat swimmer stroke so you understand the modified elements compared to the elementary side stroke.  CSS — 3 Part breakdown

The question received this week concerns how to get faster at the 500yd swim for the Navy BUDS, EOD, Diver test.

Stew, I am preparing to take the BUD/​S PST and finally learned the CSS.  I can get 50yds in 5–6 strokes and in 50 seconds or less, but my time for the 500yd is still in the high 9 minutes.  Any advice?  I feel I have the technique down, how do I maintain that pace?

CONDITIONING:  This is what I call the first step at swimming sub-​​8 minutes on the CSS 500 yd swim test.  What your stroke count /​ length and time per 50yds tell me is that your technique is capable of handling a 8:20 or less 500yds swim, BUT your lungs are not.  It is now ALL about conditioning.

Assessment Drill:  Here is a drill for you to do the next time you are in the pool.  Swim 500yds like you would for the test.  Have someone mark down your times at each lap.  We do this all the time as it tells me where you are falling off of your pace and where you need to focus your workout distances when you swim.  In fact, one of our guys currently has the exact same problem as you do and his scores were recently the following .  A typical 500yd swim will look like this for you I bet: (10 x 50yd laps) 1) ::50  2)  1:40 3) 2:30 4) 3:22 5)  4:20 6)  5:20 7)  6:20 8)  7:30 9)  8:40 10)  9:50.  

As you can see, you start off on perfect pace at 50 seconds (8:20 pace) and maintain it pretty well for 200-​​250yds.  A better split would be 4:10 obviously, but being just 10 seconds under at this point is still sub 9 minute pace.  But you fall apart on the last half of the swim.  Your average 50yd swim from 250-​​500yds is 1:00–1:10.

Here is the progression of workouts from taking a perfect technique 50yds swim at a goal pace of 50 seconds and conditioning the lungs to handle the entire 500yd swim in 8:20.  We do this with 1500–2000 yd workouts each day.

Repeat 10 times
50yds at goal pace (::50)
rest 15–30 seconds

Repeat 5 times
100yds at goal pace (1:40)
rest as needed
Cooldown technique swim- swim easy 500yds but focus on strokes per length and good kick offs the wall /​ glides.    
 
Warmup with a 500yd swim
Repeat 5 times
200yds at goal pace (3:20)
rest as needed

Repeat 5 times
100yds at goal pace (1:40)
rest 30 seconds      
Warmup with a 500yd swim

Repeat 2 times
250yds at goal pace (4:10)
rest as needed

Repeat 10 times
50yds freestyle sprint — get winded
50yds CSS at goal pace - try to catch breath doing goal pace 50s
(no rest)     

If you want to break 8 minutes- do the same cycle from the left
to right of this chart but make your pace::45 per 50 yds = 7:30 pace  
Also — start swimming with fins to get the ankles used to the SCUBA fins you will be wearing in any Navy Spec Ops training.  Build up to 2 mile swims with fins.          

Of course, change it up each day some, however you change the swim sets, make sure you are focus on your goal pace at a certain distance where you failed in your assessment 500yd test.  Put it ALL Together:  This is how it looks when you master the technique AND master the conditioning.  These particular swimmers are swimming sub 8 minutes with one flirting with 7 minute flat for the 500 yds CSS.  (video link)