The Grille ('Cricket') were a pair self-propelled guns based around the 15cm sIG 33 heavy infantry gun and fitted on the chassis of a Panzer 38(t) tank. The first of these designs used the Panzer 38(t) Ausf H chassis and featured a large, open-top, armored superstructure for the fighting compartment that extended all the way over the engine compartment. Given the obsolesence of the Panzer 38(t) by mid-war standards, it was determined that tanks sent for repairs were to be converted to the Grille when possible. The original vehicle was an interim design pending the availability of the Ausf M chassis which was specifically designed as a self-propelled mount. The new version used the newer sIG 33/2 gun but was mostly recognizable due to its front-mounted engine and smaller superstructure. Both Grille versions served with sIG companies of armored infantry regimets and served throughout the war, proving to be much superior vehicles for the sIG 33 than the earlier Sturmpanzer I. However, subsequent German SPGs would do away with the sIG 33 in favor of howitzers.

The 15cm Schweres Infanteriegeschütz 33 (Sf) auf Panzerkampfwagen 38(t) (Sf) (or Grille) was the name given to the initial variant of this SPG built on the chassis of of the Panzer 38(t) Ausf H. This was meant as an interim solution pending the introduction of the Ausf M chassis which led to the 15cm Schweres Infanteriegeschütz 33/1 auf Selbstfahrlafette 38(t) (Sf). Both recieved the SdKfz 138/1 designation. No other variants were built.