The Shinkansen received its colloquial name of “bullet train” in its early years, due to its bullet shaped front. Modern designs all have dropped this, the question is why?
Table of contents:
Naming the Shinkansen
The official name for the high speed railways in Japan is Shinkansen, which can refer to both the lines and high speed trains on them. The term bullet train comes from the early stages of planning the Shinkansen back in 1939, and comes from the Japanese word dangan ressha (弾丸列車), and is a clear reference to the bullet shape noise of the first Shinkansen train series. While the term quickly fell out of favour in Japan, abroad the concept of bullet trains lives on today. The birth of the bullet train
Having covered the naming conventions, let’s have a look into the creating of the original bullet train Shinkansen, known today as the 0-series. Proposed plans for the 0-series date back as far as the 1930s, and some construction was started in the 1940s. However, due to WWII, construction halted and was somewhat forgotten. Only near the end of the 1950s was it that Japan resumed construction. Both to alleviate passenger traffic from conventional lines that were already running at full capacity and as prestige project for the upcoming 1964 Tokyo Olympics. 
The first bullet train ride was on 1 October 1964, on the Tokaido Shinkansen between Tokyo and Osaka, just in time for the Olympics. The service was an immediate success with over 11 million passengers in the first year, the Shinkansen became famous both in Japan and abroad. Before the Shinkansen, a one way Tokyo - Osaka would take 6 hours and 40 minutes by express train, this was shortened to 4 hours when the Shinkansen opened. Today, trains take as little as 2 hours and 30 minutes for the same route. One of the main improvements to achieve this was the to change the bullet shaped nose and introduce a much longer nose, referred to as a duck-billed design. For example, the new N700S Shinkansen has a nose that’s 10.7 meters long. The reason for this change: Japans geographical situation...
Aerodynamics and tunnels
The original bullet like design worked great outside for straight routes, yet Japan is an island made of mountainous terrain that means curves to take and tunnels to go though, and lots of them! Here is where aerodynamics and how air behaves when compressed come into play, when a train enters and exits a tunnel at high speed. This causes a massive sound known as a “tunnel boom”, which can be similar in noise level to a cannon firing. Now imagine this happening multiple times an hour and anyone living close-by would be far from happy, not just that though, the sheer force of a tunnel boom has the potential to damage the train. This meant that the 0-series Shinkansen had to enter tunnels at a maximum speed of 90 km/h. 
Basically what happens is when a train enters a tunnel at high speed, the air in front of it is compressed and does not have enough time to flow past the trains body. When all released at once, the pressure causes a shockwave that goes boom!
Current designs
The first design that tried to resolve the shockwave problem was the 500-series Shinkansen, which took its design inspiration from the kingfisher bird. What’s special about the Kingfisher is that these birds travel from areas of air (a place of low resistance) to the water (a place of high resistance) without making a splash. The bird can do this because of its long, pointed, wedge-shaped beak. This inspired the engineers at the time to create a series of tests that confirmed the idea, and so the first Shinkansen train was born that had a much longer nose and a body that had a lot less air resistance. This allowed the 500-series to travel through tunnels at almost full speed. 
Newer designs like the Tokaido N700 series and JR East E5 and E7 Shinkansen series have taken the design further with record long noses spanning about 15 meters long. With future designs like the Alpha-X Shinkansen taking this trend even further.
There you have it, basically a bullet shape is not the best design when you need to move through a lot of air that can't go any other way. A long shaped nose is a much better design when having to travel through places of high air density. We hope you can come appreciate the design yourself when utilising the JR Pass in the near future.
To learn more about different types of (bullet) train in Japan, see: Types of trains in Japan.
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