The English Water Spaniel is a breed of dog that has been extinct since the first part of the 20th century, with the last specimen seen in the 1930s.
 It was best known for its use in hunting waterfowl and for being able to dive as well as a duck.
 It is described as similar to a Collie or to a cross between a Poodle and a Springer Spaniel with curly fur and typically in a white and liver/tan pattern.
The Welsh Springer Spaniel is a breed of dog and a member of the spaniel family.
 Thought to be comparable to the old Land Spaniel, they are similar to the English Springer Spaniel and historically have been referred to as both the Welsh Spaniel and the Welsh Cocker Spaniel.
 They were relatively unknown until a succession of victories in dog trials by the breed increased its popularity.
 Following recognition by The Kennel Club in 1902, the breed gained the modern name of Welsh Springer Spaniel.
 The breed's coat only comes in a single colour combination of white with red markings, usually in a piebald pattern.
 Loyal and affectionate, they can become very attached to family members and are wary of strangers.
 Health conditions are limited to those common among many breeds of dog, although they are affected more than average by hip dysplasia and some eye conditions.
 They are a working dog, bred for hunting, and while not as rare as some varieties of spaniel, they are rarer than the more widely known English Springer Spaniel with which they are sometimes confused.
The Norfolk Spaniel or Shropshire Spaniel is an extinct breed of dog since the early 20th century.
 It was originally thought to have originated from the work of one of the Dukes of Norfolk, but this theory was disproven after being in doubt during the later part of the 19th century.
 The term was used to designate springer type spaniels that were neither Sussex nor Clumber Spaniels, and attempts were made to use it to specify a breed that would later become known as the English Springer Spaniel.
Ch.
 Felicity's Diamond Jim, CD, RE (June 8, 2000 – May 6, 2011), commonly known as James, was an English Springer Spaniel, best known for being the 2007 Best In Show winner at the Westminster Dog Show.
 It was his 51st Best in Show victory, and his last, as his owners chose to retire James after the win to focus him on his work as a certified therapy dog.
 He was handled exclusively by the same handler who took Ch.
 Salilyn 'N Erin's Shameless to a best-in-show at Westminster in 2000.
 In retirement he was recognised in 2008 by the English Springer Spaniel Field Trial Association for his work as a sire and has produced many champion offspring, including Ch.
 Cerise Jesse James.
The American Cocker Spaniel is a breed of sporting dog.
 It is a spaniel type dog that is closely related to the English Cocker Spaniel; the two breeds diverged during the 20th century due to differing breed standards in America and the UK.
 In the United States, the breed is usually called the Cocker Spaniel, while elsewhere in the world, it is called the American Cocker Spaniel in order to differentiate between it and its English cousin, which was already known as "Cocker Spaniel" before the American variety was created.
 The word "cocker" is commonly held to stem from their use to hunt woodcock in England, while "spaniel" is thought to be derived from the type's origins in Spain.
Springer Spaniel refers to two different breeds of dogs, both of which are commonly called simply "Springer Spaniel":
The English Springer Spaniel is a breed of gun dog in the Spaniel family traditionally used for flushing and retrieving game.
 It is an affectionate, excitable breed with a typical lifespan of twelve to fourteen years.
 They are very similar to the Welsh Springer Spaniel and are descended from the Norfolk or Shropshire Spaniels of the mid-19th century; the breed has diverged into separate show and working lines.
 The breed suffers from average health complaints.
 The show-bred version of the breed has been linked to "rage syndrome", although the disorder is very rare.
 It is closely related to the Welsh Springer Spaniel and very closely to the English Cocker Spaniel; less than a century ago, springers and cockers would come from the same litter.
 The smaller "cockers" hunted woodcock while the larger littermates were used to flush, or "spring," game.
 In 1902, The Kennel Club recognized the English Springer Spaniel as a distinct breed.
 They are used as sniffer dogs on a widespread basis.
 The term "Springer" comes from the historic hunting role, where the dog would flush (spring) birds into the air.
The English Cocker Spaniel is a breed of gun dog.
 The English Cocker Spaniel is an active, good-natured, sporting dog standing well up at the withers and compactly built.
 There are "field" or "working" cockers and "show" cockers.
 It is one of several varieties of spaniel and somewhat resembles its American cousin, the American Cocker Spaniel, although it is closer to the working-dog form of the Field Spaniel and the English Springer Spaniel.
The Kooikerhondje (literal English translation "little cager dog" or "little caging dog") is a small spaniel-type breed of dog of Dutch ancestry that was originally used as a working dog, particularly in an "eendenkooi" (duck cage) to lure ducks.
 Kooikers were popular in the 17th and 18th century and appeared in the paintings of Rembrandt and Jan Steen.
 The breed is rapidly gaining popularity in the United States, Canada and Scandinavia, where it is still relatively unknown.
The Trigg Hound (also known as the Trigg Foxhound or Hayden Trigg Hound) is a variety of the American Foxhound, developed in Kentucky by Colonel Haiden Trigg.

Question: Which breed of dog, Trigg Hound or Welsh Springer Spaniel, were relatively unknown until a succession of victories in dog trials by the breed increased its popularity?
Answer: The Welsh Springer Spaniel