An aircraft (100; 310; 400) comprising: a fuselage having an underside; a first modular bay (106; 202;) recessed within the underside of the fuselage, the first modular bay (106; 202;) including a first modular bay interface (206, 246); a second modular bay (108, 110; 242, 244; 302) recessed within the underside of the fuselage, the second modular bay (108, 110; 242, 244; 302) including a second modular bay interface; a first plurality of payload modules (128, 132, 136, 138, 208, 210, 212) each having a respective function and a first payload interface (230, 232, 234) adapted to connect to at least a portion of the first modular bay interface (206, 246); and a second plurality of payload modules (112, 114, 116,118; 308) each having a respective function and a second payload interface adapted to connect to at least a portion of the second modular bay interface; wherein, the first modular bay (106; 202) is a central modular bay and the second modular bay (108, 110; 242, 244; 302) is a side modular bay that flanks the first modular bay (106; 202) such that the first and second modular bays are abreast relative to one another; wherein, the first plurality of payload modules (128, 132, 136, 138, 208, 210, 212) are interchangeably insertable into the first modular bay (106; 202) to enable the first modular bay (106; 202) to support the functions of the first plurality of payload modules (128; 132; 136; 138; 208, 210, 212); and wherein, the second plurality of payload modules (112, 114, 116, 118; 308) are interchangeably insertable into the second modular bay (108, 110; 242, 244; 302) to enable the second modular bay (108, 110; 242, 244; 302) to support the functions of the second plurality of payload modules (112, 114, 116, 118; 308). a fuselage having an underside; a first modular bay (106; 202;) recessed within the underside of the fuselage, the first modular bay (106; 202;) including a first modular bay interface (206, 246); a second modular bay (108, 110; 242, 244; 302) recessed within the underside of the fuselage, the second modular bay (108, 110; 242, 244; 302) including a second modular bay interface; a first plurality of payload modules (128, 132, 136, 138, 208, 210, 212) each having a respective function and a first payload interface (230, 232, 234) adapted to connect to at least a portion of the first modular bay interface (206, 246); and a second plurality of payload modules (112, 114, 116,118; 308) each having a respective function and a second payload interface adapted to connect to at least a portion of the second modular bay interface; wherein, the first modular bay (106; 202) is a central modular bay and the second modular bay (108, 110; 242, 244; 302) is a side modular bay that flanks the first modular bay (106; 202) such that the first and second modular bays are abreast relative to one another; wherein, the first plurality of payload modules (128, 132, 136, 138, 208, 210, 212) are interchangeably insertable into the first modular bay (106; 202) to enable the first modular bay (106; 202) to support the functions of the first plurality of payload modules (128; 132; 136; 138; 208, 210, 212); and wherein, the second plurality of payload modules (112, 114, 116, 118; 308) are interchangeably insertable into the second modular bay (108, 110; 242, 244; 302) to enable the second modular bay (108, 110; 242, 244; 302) to support the functions of the second plurality of payload modules (112, 114, 116, 118; 308).