AttheaccessionofJamesI。in1603，PettwascommandedbytheLordHighAdmiralwithallpossiblespeedtobuildalittlevesselfortheyoungPrinceHenry，eldestsonofHisMajesty。ItwastobeasortofcopyoftheArkRoyal，whichwastheflagshipoftheLordHighAdmiralwhenhedefeatedtheSpanishArmada。
Pettproceededtoaccomplishtheorderwithalldispatch。Thelittleshipwasinlengthbythekeel28feet，inbreadth12
feet，andverycuriouslygarnishedwithinandwithoutwithpaintingandcarving。Afterworkingbytorchandcandlelight，nightandday，theshipwaslaunched，andsetsailfortheThames，withthenoiseofdrums，trumpets，andcannon，atthebeginningofMarch，1604。AfterpassingthroughagreatstormattheNore，thevesselreachedtheTower，wheretheKingandtheyoungPrinceinspectedherwithdelight。ShewaschristenedDisdainbytheLordHighAdmiral，andPettwasappointedcaptainoftheship。
AfterhisreturntoChatham，Pett，athisowncharge，builtasmallshipatGillingham，of300tons，whichhelaunchedinthesameyear，andnamedtheResistance。Theshipwasscarcelyoutofhand，whenPettwasorderedtoWoolwich，topreparetheBearandothervesselsforconveyinghispatron，theLordHighAdmiral，asanAmbassadorExtraordinarytoSpain，forthepurposeofconcludingpeace，afterastrifeofmorethanfortyyears。
TheResistancewashiredbytheGovernmentasatransport，andPettwasputincommand。Heseemstohavebeenmarriedatthistime，ashementionsinhismemoirthathepartedwithhiswifeandchildrenatChathamonthe24thofMarch，1605，andthathesailedfromQueenboroughonEasterSunday。