First introduced on 15 February 2006, these were the first wheelchair accessible buses (WAB) in Singapore and was launched by SBS Transit with much fanfare on Service 21 (St Michaels to Pasir Ris). SBS Transit initially placed an order for 150 Euro III B9TLs and later exercised its option for a further 50 units, bringing the total purchased to 200. While some of the earlier purchases were low-floor models, it was from this point new buses began to be fitted with manual wheelchair ramps, paid with funding from the government.

They were powered by the Volvo D9A300 EM-EC01 engine (9,364cc), which meets the Euro III emission standards. Of the 200 units, 50 were fitted with 4-speed Voith D864.3 automatic transmission, while the rest were fitted with 6-speed ZF 6HP 592 Ecomat automatic transmission. SBS7321D later had its transmission changed to the newer 6-speed ZF EcoLife automatic transmission. The bodywork and interior fittings was the evolution from the prototype trial on a B10TL (SBS9889U) by PSV International and ComfortDelGro Engineering (CDGE). The bodywork of these 200 units were built and assembled locally by CDGE. A further derivation of this bodywork was later offered by MCV as the DD103.

Air-conditioning was supplied by Denso of Japan. These buses originally used plastic destination plates as a cost-saving measure. Advances in technology have since made LED-based signs cheaper, and by end of 2011 all units were fitted with EDS supplied by LECIP.