By the mid-1800s most steam locomotive tenders consisted of a fuel bunker (that held coal or wood) surrounded by a "U" shaped (when viewed from the top) water jacket. The overall shape of the tender was usually rectangular. The bunker which held the coal was sloped downwards toward the locomotive providing easier access to the coal.

The ratio of water to fuel capacities of tenders was normally based on two water-stops to each fuel stop because water was more readily available than fuel. One pound of coal could turn six pounds of water (0.7 gallons) to steam. Therefore, tender capacity ratios were normally close to 14 tons of coal per 10,000 gallons of water. One exception to this were the NYC tenders which were designed to pick up water at speed from track pans. These tenders had a much larger coal to water ratio.

Other factors which determined the size of tenders were turntable length. Some railroads bought large locomotives with small tenders so that they could still be turned on their existing turntables. In many cases, these tenders were replaced with larger ones as larger turntables became available. Construction styles also determined tender size. In 1927 the first solid steel cast tender frame made it possible to attach a single large tank called a "water bottom". These tenders could hold 1,500 to 2,000 more gallons of water then previous tenders could.

There were a number of variations of tender design. This page will describe a few of them.

Typical switch engines spent as much time waiting as they did switching. They didn't require large tenders. Tenders for such locomotives were designed with a sloping rear -- reducing the capacity for water, but allowing better visibility to the rear. The Pennsylvania Railroad (and many others) had many switchers with slopeback tenders.

During the early days of Mallet and articulated locomotives, whale back (sometimes called "turtle back") tenders were used. Whale back tenders consisted of two separate tanks (the leading one for oil, the aft one for water). They had greater capacity than the old square tanks. They looked like a half cylinder laying on its side. They were some of the ugliest tenders. Many early Souther Pacific cab-forwards used whale back tenders.

A round tank has several advantages over a rectangular tank.

• A round tank holds more than a rectangular tank of the same surface area.
• A round tank (a cylinder) is stronger than a rectangular tank (a box).
• A round tank is lighter than a rectangular tank of the same capacity (partially because a rectangular tank requires a great deal of internal bracing).

On May 31, 1901, a patent was issued to Cornelius Vanderbilt for a tender with a cylindrical water tank (Cornelius was the great grandson of the Commadore). Some railroads went for Vanderbilt tenders in a big way. Others did not. Railroads that adopted the Vanderbilt style tender for many of their steam locomotives include:

• Baltimore & Ohio
• Canadian National
• Grand Trunk Western
• Great Northern
• Southern Pacific
• Union Pacific

Seven of the B&O T-3 class 4-8-2s, built by the road between 1943 to 1948, were retro fitted with large vanderbilt tenders, mounted on six wheel trucks. It is conceivable that these tenders were salvaged from scrapped locomotives. The B&O was a large user of Vanderbilt tenders. They had some very odd ones which had three four-wheel trucks, rather than two six-wheel. These may have been applied to 2-8-8-0 engines.

The PRR made good use of "long haul" tenders. The PRR long haul tenders generally had two 8-wheel trucks. The T class 4-4-4-4 duplex locomotives were equipped with Class 180-P-84 tenders that carried 19,200 gallons of water and 42.5 tons of coal (221 tons total weight). The S-1 class 6-4-4-6 duplex locomotive was equipped with the same class tender but with 24,230 gallons of water and 26 tons of coal capacity.

The AT&SF 2900 Class also used long haul tenders with 8-wheel trucks. Their tender capacity was 24,000 gallons of water and 7,000 gallons of fuel oil.

The centipede (sometimes called pedestal) tender was introduced in the late 1930s. What gives this style of tender its name is the number of wheels it uses. A centipede tender is rigidly mounted to five axles (ten wheels) which are allowed to move laterally. There is also a four-wheel leading truck that is able to swivel, for a grand total of 14 wheels. This tender is also sometimes referred to as a "pedestal" tender because of the shape of the container -- slightly smaller at the bottom which had "pedestal" for supporting the five rigid axles.

The centipede tenders used on the Big Boys were designed so that they could haul a 3600 ton train from Ogden to Echo (40 miles) without stopping. This required 24,000 gallons of water and 28 tons of coal. The second series of Big Boys were equipped with 25,000 gallon/28 tons tenders which were originally designed for the 1942 Challengers. The change in capacity was not simply due to a larger tank. Instead, the first set of Centipede tenders used a novel (and probably unique) system for lubrication of various points of friction which included axle bearing box pedestal wear faces, front truck center pin, etc. This was accomplished via fitting of a Nathan DV-7 mechanical lubricator which was driven by the stoker engine. The box for the lubricator and other related accomodations resulted in the the displacement of approximately 1,000 gallons of capacity. These systems were removed not long after construction all all of these tenders were then probably brought into the same classification, being 25-C (twenty five thousand gallon-cylindrical).

Centipede tenders were used on locomotives that had enormous fuel requirements. These locomotives included:

• Boston & Maine Mountains
• Denver & Rio Grande L-97 Challengers
• Duluth, Missabe & Iron Range Yellowstone
• Clinchfield E-2, E-3 Challengers
• Great Northern Z-6 Challengers?
• New York Central Niagaras
• New York Central Hudsons (Class J-1a 5266-5274 at times, Class J-3a after 1944, photos)
• Northern Pacific A-5 Northerns
• Northern Pacific Z-6 Challengers
• Spokane, Portland & Seattle Z-6 Challengers?
• Union Pacific Big Boy
• Union Pacific Challenger
• Union Pacific FEF-2,3 Series

Small switch engines that were only operated in a yard close to a fueling site didn't need a tender. Instead, they carried a "U" shaped water tank that was draped over the boiler and a small bunker behind the cab for coal or oil. These were called tank engines. Sometimes the water tank was split in two and were on either side of the boiler.

A "T" is added to the Whyte system of wheel classifications to denote a tank locomotive. For example, an 0-6-0 would be a normal switch engine with a tender. An 0-6-0T would be a switch engine with a "tank" instead of a tender. Sometimes 0-6-0ST was used. The "ST" stood for Saddle Tank. Sometimes, a tender was added to a tank engine to provide extra range. This type of configuration was denoted by 0-6-0T-T.

Forney or "rear tank" type locomotives sometimes went under the designation of 0-4-4RT. The "RT" of course stood for Rear Tank.

There is another type of tank engine arrangement not typically found on North American built engines (but very common on European built ones). This would be a "Well Tank" locomotive. The water was carried in a tank built into the frame of the locomotive. Usually these were small narrow gauge switchers. An 0-4-0 example would carry the designation 0-4-0WT. The popular LGB German 0-4-0 G scale engine is a model of one of these Well Tank locomotives.

Normally, freight operations required both a head-end brakeman and a brakeman at the rear of the train. Often, there wasn't a lot of extra room in the cab. The fireman didn't always like to share his seat with the brakeman and there wasn't really enough room to stand without getting in the way of the fireman. By 1937, new locomotives were built with enough room to seat the head-end brakeman in the cab. Older locomotives were modified during shopping with a small cabin on the top of the tender for the head-end brakeman. This was called a "doghouse".

Auxiliary tenders or canteen cars, used to supplement water capacity on road locomotives and were reasonably common during the steam period. One of the best examples of their use is behind N&W class A locomotives on the generally down grade run between Williamson and Portsmouth. The use of these cars enabled the N&W to bypass two water loading points where the start would have been made on an upgrade, thus enabling the N&W to run substantially heavier trains.

Auxiliary tenders are also commonly used in excursion service by today's surviving steam locomotives. Often, it is only the "mainline" operations that require them to increase the distance between watering locations. Sometimes a tender is converted to carry the extra water. In the case of 3985 and 844, a "Big Blow" tender was converted for this purpose. The auxiliary tender for the SP&S 700 is from a Great Northern S-2 4-8-4. It was built to hold 17,500 gallons of water and 5,600 gallons of fuel.