Naval Gun fire Ballistics and the pursuit of Target Archery.
This article by LCDR Damon Craig, JP, RAN (rtd), CPEng, etc.

This is my second article on Archery. I find it more and more difficult to avoid my past role as sea going WEEO when I get further into the field of target Archery. First some assumptions before we proceed…

I say target Archery versus the Art of Archery as there is a distinct difference between seeking the perfect shot in the art of Archery and this may only every happen once in a lifetime (if ever) versus the scoring of target Archery where for a set of complex reasons there may be a wild disconnect between skill and scoring.

I was a very dedicated Weapons Engineer and deployed on warlike service numerous times with the Royal Australian Navy. I left under medical grounds but whilst I do not have access to current information I remain bound by disclosure rules. This article does not breach that obligation and obviously there may be a few gaps in the story for this reason.

There are some mechanical and philosophical difference between single string Archery and compound bows and I will generally assume that these differences are understood.

There is a common concept of the engagement sequence in Naval Gunnery and it is generally linked to the shot cycle in Archery. The engagement sequence is close held by each surface force and the Archery shot cycle is the focus of my other article.

So what this article will cover is the science of ballistics and how this may enable the further pursuit of target Archery. As a point of credibility, the basic engagement orders of a gunnery engagement have three main points being that they have a stable target on radar, the gun pointing at the target and that there is a deliberate order to loose ammunition towards the target. There are a bunch of safety calls that are used in training and as it is general that we train the way we fight these are usually enduring concepts.

This is no different to target Archery. Part of my warm up routine is to check the lane and range for safety and lighting and check with other Archers at the distances, arrow count and bow type they are using. This is an essential part of safety and my shot cycle timing but also just part of being a good bowman at my club. Hopefully you get there is so much more than just the scored arrow in this note.

Just to round out my comparison to gunnery most Archery clubs and governing bodies have clear safety rules about only pointing towards targets and a series of noises or calls to open and close the range, even at short notice.  

I got dragged into a conversation one day on layout of fletches on arrows; be they straight, curved or helical. My short answer is under 20m then I would need a very good reason to move away from straight fletches, at longer distances curved or helical make more sense but there is a trade off with drag and speed, this will have a huge impact on target achievement so that needs to be understood.

It was at this point that I need to remind people that on a single bowed set up, the arrow experiences maximum thrust at the time of release, this thrust drops off until the arrow leaves the knock. The obvious issue is that the arrow will flex and twist; it is mostly unavoidable but can be reduced with choice of hardware and equipment set up. A compound or multi stringed bow will give maximum thrust just before the arrow leaves the knock. This not only allows the Archer to be on draw for longer periods but also reduces the deformation of the arrow with a huge impact on targeting.

This deformation of the arrow is usually short lived but across the entire flight it will become an issue. In gunnery we talk of direct fire being the very straight trajectory of the bullet in its first few seconds of flight. The bullet is being impacted by gravity and drag but the velocity is so high. As the velocity slows then the ballistic or curved path is more of an issue. For very long times of flight the pullet may effectively stop any flying or ballistic properties and tumble through space as a dead but fast mass. This tumble is also part of Archery at distance.

These three phases are mirrored in Ten Pin Bowling where the ball will slide, then roll and then tumble or hook. Modern reactive balls make full advantage of this and the asymmetric nature of the balls core is used fully to make a dramatic hook. This all has to be tuned very carefully to the Bowlers style and speed. Target Archery is not free of these concepts and I pose that an arrow is most effective if the target is placed beyond the distance needed to overcome initial arrow deformation but before the arrow starts to wobble. As compound bows have very little wobble and higher exit speeds the effective range window for a compound bow is much greater. Foe a single string bow, this effective range starts further down the range, but also, given the lower speed on exit, the range window closes sooner. This is why getting lower deformation is a great aim for recurve Archers. It must be noted though that a stiffer arrow may appear to deform less but may not recover as well making targeting harder. Helical vanes may help the arrows recover and suffer less from tumble.

There is an Archer that frequents my club and he believes that more arrows down range is a good day at the club, he scores every arrow and leaves only when he has flown the required 300 plus shots. His note book is full of scores but strangely lacking in much other data like temperature, time of day, humidity. These are all used by Navy in order to calculate a fire control solution for the engagement. These are the cornerstone of Naval Gunnery and should be understood. So how do these lessons from big gunnery impact on our discussion of Archery? I comment as follows…

Input of barometer will have an impact on the amount of aim particles that will be acting on the arrow during it’s time of flight. Higher density will reduce the range of the arrow as will humidity as it is a measure of the number of heavy water molecules that are suspended in the air between the Archers line and the target.  

Temperature will have an impact on the deformation of the arrow and the performance of the limbs of the bow. Higher temperature will depower the limbs and make arrows more flexible. The general temperature of the range will impact on the Archer most likely the increased joint movement will promote over drawing or lead to fatigue that impact on targeting. This is a direct impact to big gunnery where the most important temperature reading is the powder temp prior to firing as the speed of the ignition of the powder is impacted and directly impacts on Muzzle Velocity of the bullet leaving the gun. There is a possibility in modern Archery that draw length can change and affect the speed of the launched arrow. The nature of the compound bow and the use of the clicker in recurve Archery accounts for this. I cannot work with the clicker so this is one variable I must fight in my draw cycle.

Latitude, Longitude and direction of travel are very important for Naval Gun Fire. Hemisphere information is important to account for the curvature and rotation of the earth. The Bullets can have very long times of flight and the impact to targeting must be known. Firing with or against the rotation of the earth will reduce or extend range. The firing direction in the North South domain will be impacted due to the rifling or spiraling nature of the barrel that imparts spin on the projectile; this spin may help or hinder its targeting. The impact of this is impacts by the distance from the equator or Latitude.

Wind speed and direction is useful in Gunnery and should be applied in Archery. This is often a simple dial in change to most Archery sights and being the only targeting change that should be made in competition for a properly tuned set up, it often accounts for many of the above changes in one simple dial. In Naval Gun Fire we can gather metrological data to give us different wind speed and temperature data at various heights above the war space. Modern combat systems can make use of this to adjust for this for better targeting probability. The roll and pitch of the ship is also accounted for whilst it would be great to predict even a few second ahead for the ship motion, but for most cases a constant adjustment process is fine. There is a great area of work around the relative motion of the target. This is handled by Combat Systems that effectively aim ahead of the target. Time of flight of rounds is important. In Target Archery the aim point of still and even in hunting it is rare to acquire a moving target. For this article this variable is acknowledge and set aside.

So in summary there is something very satisfying for me in being on time and on target in Archery. This probably comes from both the need and the pride in being successful in my role as a Weapons Electrical Engineer Officer at sea. There is a certain element of improbability in Naval Gun fire but with skill and dedication we can manage all these errors to put a round to a 4 dimensional space. I remember at the time learning that many historical Fire Control Systems could not account for all the above variables so they effectively functioned on massive look up tables to improve speed and reliability of computing where to point the barrel. Now a days there is more than sufficient computing power to find solutions and verify results well within an appropriate time frame.

“Hit first and Keep Hitting”  
Painted on the side of a Gunnery School Building at HMAS CERBERUS.