The site, launched in 1999, has seen a huge increase in customers since it embarked on a £2m television advertising campaign last year.
It needed a scalable and stable platform to support the growth, said Andrew Probert, IT director of The Admiral Group. "We did not have the stability when we launched Elephant as we started with some very crude HTML applications," he said.
"We were a big user of the AS/400 platform [now iSeries] so Websphere was a natural progression, particularly as we did not think other platforms were as stable."
The Websphere platform means the Elephant site is quick and easy to use, according to Probert, which, he said, has been key to its success. "Insurance is a boring process for consumers with a whole host of lists to fill out so the quicker and easier it is the better.
"We have pushed the Internet harder than most other insurers and [the Admiral Group] now conducts about one-third of its business over the Net. This is compared to about 5% for the industry as a whole."
Admiral is looking to build on the success of the site by extending the number of applications available.
IBM last week said there has been a substantial increase in UK customers using Websphere on the iSeries platform.