When you think of the cardio events most tactical personnel should be capable of doing, you may think of running, swimming with fins (or without), and carrying heavy equipment gear (rucking). Mix them all into a killer cardio day by doing what we call the Spec Ops Triathlon.
Over time, build up your distances and times involved in each event such as:
Run 3 miles – Swim 1000m – Ruck 3 miles (25-40#)
Build up to 5 mile run, 1 mile swim, 5 mile ruck over time.
This is a pretty standard distance for the Tactical Cardio event, but you can turn it into a much more well-rounded set with the right progressive build-up routine. You can also rearrange the order of the events and start or finish with the swim. The goal is to get in 90-120 minutes of cardio spread into these three events.
If you cannot swim, try replacing that portion with another non-impact cardio activity like rowing, biking, or elliptical just to do some cross-training.
You can also mix in some PT exercises in between the events as well. My workout group likes to add in big max reps sets, or pyramids of calisthenics, or even the Devil's Mile. Adding in some injured-man drills make for a useful skill practiced for a few miles of the run.
To stay good at these cardio exercise, you have to practice them. This is a one-stop shop method that can really boost your cardio abilities.