Imagine a scenario where you are running while getting shot at and you see a pool that is about five foot deep. From hours of watching action movies; you know that jumping into water is a good way to survive the bullets. However, is it actually true? Will it suffice in real-life and help you save yourselves from the bullets flying towards you?
We decoded the famous movie scenes, and it turns out that they are not that far from the truth and principles of physics. The first thing to consider in such a situation is the drag. The drag on a bullet is the primary reasons behind the reduction in its speed, and even in the air, the bullet is experiencing drag. Now, water has a density that is about 800 times more than air; thus, the bullet will only be able to travel for a few feet at most.
During D-day, bullets that were being fired from the MG-42 were only able to penetrate the water to a depth of 2.5 feet. It is important to note that the bullets being fired from the MG-42 escape the barrel at speeds of about 3,000 feet per second. The next factor is that of speed, and this is where things might get trickier. As per the Drag equation on Wikipedia, the faster a bullet is traveling initially, the slower it will be once it enters the water.
This explains why the bullets from MG-42 were only able to achieve a depth of 2.5 feet, but it also implies that small calibers can achieve greater depths of up to 8 feet. Moving on, the next factor to keep in mind is that of angle. Unless someone is firing from the sky, you will not be fired at from above the water, meaning that the bullets will enter the water at an angle. If the bullet is being fired from an angle that is less than 30 degrees than the bullet won’t go further than 3-5 feet in theory.
The last thing to consider is the ricochet. Bullets that are being fired at a lower angle might result in a ricochet, thus helping you not get hit. As a conclusion; water can help you stay safe from a hail of bullets, but there are many variables that lower your probability of not getting hit. For instance; you might end up in a pool that is not deep enough, or you might run out of oxygen.