In the late-1970s, DCNS of France developed a new cost-effective, export-friendly diesel-electric attack submarine to succeed the 1960s-era Daphne design. This became the Agosta-class and the new boats were eventually taken into service by the French Navy as well as the navies of Spain, Malaysia and Pakistan. For the Pakistan Navy, two distinct batches were made, one based in the original Agosta-70 standard (these two boats were originally bound for South Africa, pre-embargo) and the other in the improved Agosta-90B standard (three boats in all).
Of the three Agosta-90B-class boats taken into service, only the first was constructed in French waters - the remaining two were built in Pakistan and future upgrades were handled with the assistance of specialists in Turkey. These became PNS Khalid (S137), PNS Saad (S138), and PNS Hamza (S139)
PNS Khalid was commissioned from the Agosta-70B-class stock on September 6th, 1999. She was constructed in French waters by DCNS and named after Khalid ibn al-Walid, a companion of Muhammad. At its core, the boat was developed along conventional lines, the propulsion scheme being centered on a diesel-electric combination arrangement allowing for basic surfaced and high-speed submerged travel at 12 knots and 20.5 knots, respectively, out to ranges of 8,500 miles.
The boats were given a basic profile with the sail being fitted ahead of midships, dive planes seated forward at the bow, and a cruciform plane pattern set at the stern near the single shaft. The sail was finished with smooth, rounded edges and wide when viewed in the side-profile, sloping along its aft-end. The nose cone was left somewhat blunt when cutting through the water at speed and a sonar fit was noticeable as a protrusion at the bow. The boat was made capable of taking a crew of about forty-one men with dimensions including a running length of 291.9 feet with a beam of 19.7 feet. Displacement is 1,525 tons when surfaced and 2,085 tons when submerged.
The attack submarine was given the usual surface-search, radar and sonar fits consistent with vessels of this type (including internal sonar as well as a towed array unit) and armament became 4 x 21" bow-facing torpedo tubes also having support for the American Harpoon anti-ship missile and a naval mine dispensing quality.
As of this writing (2018), PNS Khalid (S137) remains in active service with the modern Pakistan navy fleet, leading her group of three boats.